Hope you know the diffrence between U, T, L, S, -S, H and pi cases becuse you need to know to understand this.
For H and pi cases look at the four corner stickers that are in the U layer, compare the colours, the patterns are distinctive for each case.
Those are the easiest cases to recognise, just look at U!
A little harder are U and T but not much. For those you always has got two corners oriented on one side, first look at the two stickers at that side and then at the two stickers that are unoriented corners in the U layer and you find your patterns.
For L cases you look at the two unoriented stickers in U and at both side stickers of one of the other two oriented corners.
For S, and -S, well, let's not talk about those please
No, I'm joking =) but S and -S are the worst cases, first thing, there are totaly 12 S and -S cases = a loot of room for confusion. The way I do S is: find two stickers of opposite colours (ex blue and green) in the U layer and then find at least one of the others (blue or green) on the side somewhere (hint, no perm (Sune) and diagonal perm has got diagonal stickers in U, the others are adjacent).
Edit: when you can recognise the cases fairly good, then use a 2x2x2, go colour independent and solve one layer, try to find your case and do COLL to solve LL. That's how I learned recognition for real, best practice I can think of.
