Make sure you know your color scheme really well. A lot of times, you will solve your cross and then do D, D', or D2 to line it up with the centers. Try to spot the four pieces you need all at once, and think of them as a whole. Keep track of what moves affect what pieces, and try to use this to your advantage. A lot of it is just practice and learning to see what tricks you can use. Here are some examples (scramble with yellow on top, orange in front):
R2 D' U F' U' D' L R' F L2 R2 F' D F2 B D' B L2 U D2 F R' B' D2 F
The first thing I see is the red piece. Most of the time, whenever a cross piece is in the D layer and it is oriented correctly, I don't move it at all. I try to work around it and build off of that piece. The next thing I see is the blue piece in FL. I see that if I do F', then both my blue and red pieces will be solved. Here's where you can use a little shortcut, and this is where thinking of all the pieces as one group is important. I see the orange piece in UR. If I do U and then do F' to put that blue piece in, that sets up my orange piece to be put in place. So, so far my cross is U F' L. Now the last piece, green, in BL, is not exactly in a favorable spot. I see that it is lined up with its opposite center. Being able to see opposites is very important in cross solving. Anyway, the way I would solve this piece would be to do D' so that the rest of my cross pieces are with their opposite centers. Then R will solve the green piece. Finally, D2 lines everything up with their correct centers. So my whole cross is U F' L D' R D2. Now, once you get better at the cross, you can add even more tricks to it. For example, in this case, the blue-red edge is solved while you are making the cross. I saw this during pre-inspection, but you can also see this while you are solving the cross (though you have to think very quickly if you do it this way). Anyway, since I know that that piece will be solved, and since I am solving my cross on opposite centers and then lining it up, I have the opportunity for a nice extended cross. So while I am making the cross, I am looking for the white-blue-red corner. So I do U F' L D' R. Before I do D2 to line everything up, I look for it real quick, and conveniently enough it is right where I want it to be: UFL. So, now I would do y' R U R' to solve that corner, then do D2 to line everything up, and you've got an extended cross. I try to do something like this every time I finish my cross with a D move and a piece of a pair is solved during the actual cross making process.
Another thing you want to keep in mind is that once you know what moves you are going to do for your cross, make sure you do them quickly. I like to slow down a bit on my last move or two to try and spot a pair, but you should not spend more than 2 seconds on the cross. Likewise, the cross should NEVER be more than 8 moves. 99.95% of all crosses can be solved in 7 or fewer moves, the remaining .05% can be solved in 8. Just something to think about.
Like everything with cubing, after a lot of practice you will just start to see these things instantly. I hope this actually helped and didn't confuse you, heh. Good luck!
h43r: As far as I know it's only DanH who has taken the effort of explaining the cross in depth, do you guys know any other site?
