Skimming   
Skimming is the most rudimentary type of reading. Its object is to familiarize you as quickly as possible with the material to be read. You may use it for entire books or for shorter sections

. You leaf through the material looking at titles, subheadings, illustrations, maps, and charts. You are trying to become familiar with the subject matter. Remember, both speed and comprehension  depend on familiarity. The more comfortable you are with the manner in which the material is presented, the faster you will move through it and the more you will retain. Two to three minutes is ample time for a chapter, ten to fifteen minutes for a book.

Skimming may also be used to search out certain short passages you have lost. Your eye should race over the pages looking for clues which will help you narrow down the probable location. Though you feel completely lost, the act of skimming will refresh your memory and lead you to the passage. Trust your memory. If it says upper left-hand corner, look there first. With practice you can develop a memory which will allow you to recall the exact location on a page of a piece of information. After that, patient speed will do the rest. Skimming before you start is valuable for any type of reading, even pleasure reading, except perhaps for mysteries.

Skimming is used to quickly identify the main ideas of a text. When you read the newspaper, you're probably not reading it word-by-word, instead you're scanning the text. Skimming is done at a speed three to four times faster than normal reading. People often skim when they have lots of material to read in a limited amount of time. Use skimming when you want to see if an article may be of interest in your research.

There are many strategies that can be used when skimming. Some people read the first and last paragraphs using headings, summarizes and other organizers as they move down the page or screen. You might read the title, subtitles, subheading, and illustrations. Consider reading the first sentence of each paragraph. This technique is useful when you're seeking specific information rather than reading for comprehension. Skimming works well to find dates, names, and places. It might be used to review graphs, tables, and charts.

Scanning
Scanning is a technique you often use when looking up a word in the telephone book or dictionary. You search for key words or ideas. In most cases, you know what you're looking for, so you're concentrating on finding a particular answer. Scanning involves moving your eyes quickly down the page seeking specific words and phrases. Scanning is also used when you first find a resource to determine whether it will answer your questions. Once you've scanned the document, you might go back and skim it. When scanning, look for the author's use of organizers such as numbers, letters, steps, or the words, first, second, or next. Look for words that are bold faced, italics, or in a different font size, style, or color. Sometimes the author will put key ideas in the margin. Similarly, scanning skills are valuable for several purposes in studying science. First, they are an aid in locating new terms, which are introduced in the chapter. Unless you understand the new terms, it is impossible to follow the author's reasoning without dictionary or glossary. Thus a preliminary scanning of the chapters will alert you to the new terms and concepts and their sequence. When you locate a new term, try to find its definition. If you are not able to figure out the meaning, then look it up in the glossary or dictionary. (Note: usually new terms are defined as they are introduced in science texts. If your text does not have a glossary, it is a good idea to keep a glossary of your own in the front page of the book. Record the terms and their definition or the page number where the definition is located. This is an excellent aid to refer to when you are reviewing for an examination, as it provides a convenient outline of the course).

Secondly, scanning is useful in locating statements, definitions, formulas, etc. which you must remember completely and precisely. Scan to find the exact and complete statement of a chemical law., the formula of a particular compound in chemistry, or the stages of cell division. Also, scan the charts and figures, for they usually summarize in graphic form the major ideas and facts of the chapter.

Extensive 
Reading extensively means reading widely and in quantity. It means reading large amounts (often of what we find intrinsically interesting) with the main aim of getting a global understanding of what you are reading. Palmer makes the distinction between intensive reading (1968:137) which often refers to careful reading and possibly translation of shorter, more difficult foreign language texts with the ultimate goal of complete and detailed understanding. It is often the case that intensive reading is the only kind of reading that students do in the language classroom. As Dupy, Tse and Cook explain, This may be because it is largely associated with teaching reading (and other) skills and for the purpose of disassembling text for later detailed scrutiny. This is often a slow, difficult, painstaking process which is more focused on the meaning of individual words or sentences containing whatever discrete grammar point the students are supposed to be learning that day. Many students consequently associate reading in English with this approach and are therefore (understandably) reluctant to engage in reading outside of class.

Brian Seaton (1982:150) suggests that extensive reading may begin with short illustrated anecdotes, and on to short stories written in graded language that the learner can be expected to understand without great difficulty. Extensive reading presupposes that the learner reads the text without difficulty and if possible for pleasure.In a recent survey conducted by the students themselves in one of my classes on the subject of reading, (appendix 1) several people reported they liked reading in English 'what they could read fluently and without having to use a dictionary every three words.' Helgesen, M (1997) backs this up by suggesting that an average of three or four unknown words per page, or less, means a book can be read fluently. Dictionaries should not normally be consulted as this disturbs fluent reading.

By reading extensively, these learners recognize that they can improve their vocabulary and comprehension, and also recognize the need to read something they can easily understand and have an interest in. Ronan Brown (2000) insists that the more learners read, the more skilful and fluent they become. He argues that the bottom-up process of instantaneous word recognition, upon which true comprehension depends, is the result of practice.Thus, by engaging in reading extensively in what the learner is interested in, utilizing a top-down process, where the reader brings in outside knowledge and interest and is reading for global understanding, the development of a large sight vocabulary is exercised and automaticity of decoding is spurred on. This is of course only true if what is being read is largely understandable to the reader to begin with. If the small amount of learning of a word is not soon after reinforced by another encounter, then that learning will be lost (Nation, 1997). In an article on teaching vocabulary,

Intensive
The Intensive Reading Technique is reading for a high degree of comprehension and retention over a long period of time.  It is basically a study technique for organizing readings that will have to be understood and remembered.  One may have good comprehension while reading line-by-line, but REMEMBERING is what counts.  Intensive reading is not a careful, single reading, but is a method based on a variety of techniques like scanning, the surveying technique of planning your purpose, and others.
Principle of extensive reading
Overview, purpose, questions, reading, summarize, test, and understanding are the seven procedures that cover the method, for very effective reading for detailed comprehension and long retention.

Reference
Bright, J.A., & McGregor, G.P. (1970). Teaching English as a second language. London: Longman.
Broughton, G., Brumfit, C., Flavell, R., Hill, P., & Pincas, A (1978). Teaching English as a foreign language. London: Routledge & Kegan Paul.
Brown, D.S. (1988). A world of books: An annotated reading list for ESL/EFL students. Washington, DC: TESOL.
Brumfit, C. J. ( 1978). The teaching of advanced reading skills in foreign languages, with particular reference to English as a foreign language. In V. Kinsella (Ed.), Language teaching and linguistics: Surveys (pp. 1 73-184). (Centre for Information on Language Teaching and Research and English Teaching Information Centre of the British Council. Cambridge: Cambridge University Press.
Brumfit, C.J. (1979). Readers for foreign language learners of English (ETIC Information Guide 7). London: The British Council.
Brumfit, C. (1984). Communicative methodology in language teaching: The roles of fluency and accuracy. Cambridge: Cambridge University Press
Carroll, G.R. (1972). The battle for better reading. In H.B. Allen & R.N. Campbell (Eds.), Teaching English as a second language, a book of readings (2nd ed.), (pp. 178-184). New York: McGraw-Hill.
Champeau de Lopez, C.L. (1989). Improved reading through writing. TESL Reporter, 22(2), 23-26.
Clarke, M.A. (1979). Reading in Spanish and English: Evidence from adult ESL students. Language Learning, 29, 121-150.
Clarke, M.A. (1980). The short circuit hypothesis of ESL reading--or when language competence interferes with reading performance. Modern language Journal, 64, 203-209.
Cooper, M. (1987). Conference report: 11th world congress in reading. Reading in a Foreign Language, 4, 71-77.
Dalle, T. (1988). Reading journals: Solving the problem of input in the ESL composition class. TESL Reporter. 21, 23-26.
Davies, A (1984). Simple, simplified and simplification: What is authentic? In C.J.. Alderson & A.H.. Urquhart (Eds.), Reading in a Foreign Language (pp. 181-95). New York: Longman.
Davies, A, & Widdowson, H.G. (1974). Reading and writing. In J.P.B. Allen & S.P. Corder (Eds.), The Edinburgh course in applied linguistics, 3, Techniques in applied linguistics (pp. 155-201). London: Oxford University Press. .