Many IELTS books talk about 'skimming' and 'scanning' to find answers in the reading test. But the danger is that students focus more on these techniques than on the passage that they are reading, with the result that they often miss the answers by skimming or scanning past them!
Here's some simple advice:
Skimming basically means 'reading very quickly'. Only skim if you are looking for a distinctive word that doesn't have any synonyms e.g. "Manchester".
Scanning basically means 'looking for something without reading'. Only scan if you're searching for a number e.g. "1999".
For all other questions, forget about skimming and scanning; just read the passage carefully at normal speed.