There are three ways to tell if a fresh pineapple is ripe and ready to eat.

1) Check the appearance. First of all, the colour doesn't have to be yellow. Some pineapples stay green even when they're ripe. But you should look to make sure there is no obvious mold growing in any of the creases and there shouldn't be too many wrinkly brown or withered bits. The leaves on top should be  green and not dried out or brown, except a tiny bit at the tips.

2) The smell should be sweet. If you can't smell anything yet, it's probably not ripe.

3) Try pulling out one of the inner top leaves. The leaves should resist a bit, but pop out with a slight tug. You should have to brace the pineapple with your other hand, but not have to yank on it hard. If it falls out too easily, your pineapple may be starting to rot.