My Mathematics Olympiads are approaching So I have not started the preparation yet. I need to have a better resource for +2(11th or 12th class basically a high school student) Olympiads so if you have any suggestion pls go ahead :)
The UK Mathematics Trust has published some books that may be suitable and are widely used in the UK: 'A Mathematical Olympiad Primer' and 'A Mathematical Olympiad Companion' by Geoff Smith. You can find them here. They are designed for help students prepare for the British Mathematics Olympiad rounds 1 and 2.