what are some good techniques, approaches to find defects in a web based application, which would be found in basic testing?
thanks.
Check out the test heuristics cheat sheet:
http://testobsessed.com/wp-content/uploads/2011/04/testheuristicscheatsheetv1.pdf
This will give you some ideas of what types of things to look for when testing a given type of system. For example, when testing something with an input, do boundary testing (test the limits: what happens when you input nothing? what happens when you input too much data? etc.)
Best approach would be the understand the requirement or the situation and test accordingly.