Hi! I was having trouble with cross about two months ago, but now I'm able to one look a cross fairly consistently. First of all, what do you mean by messing up the centers? Second of all, make sure you practice just making cross, don't bother solving the whole cube. To start begin slowly by looking at the cube and writing down a cross solution. idealy it should be under 9 moves since any cross can be solved in under 9-8 moves. after writing down a solution, try it and repeat. eventually, you can start memorizing the the solution and the process will become intuitive. hope this helps. Youtube is also a great resource for this kind of stuff. my method is very original, but it has helped me to succeed.