Firstly, this is a stickied article which you should definitely consider reading on the 'how to' study.Be more specific about questions that are 'too easy'. What questions are you doing? Are they from a specific textbook?
Fact is, maths is a skills based subject and continuously practicing and doing questions is the best way to get better at it. Without any assessment tasks really close by, you shouldn't be restraining yourself from looking at how the textbook does questions either. Sometimes, just looking at how a textbook does a question, whilst you do another one that's similar (i.e. probably just different numbers) can train this ability.
And come exam preparation time, you shouldn't be relying on the textbook either. You should be doing as many questions as possible from past papers. Why? Because they reflect the style of exam questions better than anything else.
If you're only doing questions too easy, you need to just force yourself out of it. If you do try harder questions and just don't progress, then you need to break things down. In maths, it is quite common that a question draws on concepts from multiple topics, which is something to be prepared for.