Best way to stop making silly mistakes?

Hey all,

I'm getting frustrated, because right now the only place im losing marks is silly mistakes. and i mean silly mistakes, like reading a - as a + sign or blatantly ignoring some information in a question.

Whats a good way of not making silly mistakes? because doing past papers, ive realised its becoming a big problem for me. Ive never had this problem before so im lost on how to fix it.

Thanks