Older puzzles placed a lot of emphasis on literary knowledge. Since about 1950, there has been a loose alliance of setters who are concerned about ensuring that their clues are fair to the solver. Although there is no universally agreed set of rules about fairness, this concern seems to have improved cryptic puzzles in general. When I say 'solving', maybe I should say 'attempting to solve'. You can't learn to solve cryptic puzzles just by reading web sites or books.
Real progress requires regular practice.
This practice will inevitably include making mistakes, and not getting very far with some puzzles. Regular' means daily if possible. If you attempt less than one puzzle a week, progress will be slow. Crossword terminology You're not intended to read this glossary in full right now. Have a quick look, especially if you're new to this game, and refer to it if the cryptic crossword jargon baffles you later on.