Practice, practice, practice! You've got to learn a whole new way of moving around and keeping track of where you are, and that's only going to come with time. So keep practicing, and have fun!
The one greatest bit of technique help I found when learning doubles was a description of how to "crabwalk" across the pad. When going across the top row (left L-T-R, right L-T-R, twist and turn so you are always alternating between your left and right feet, turning the shortest way so you don't end up spinning like a ballerina. Same with the bottom row. (On the top row, left foot LL arrow, right foot LT arrow. Moving to the right. L LR, R RL, L RT, R RR.) That eliminates the awkward lurching from side to side that can happen if you try to doublestep while crossing over. Sometimes, if nobody's at the arcade, I'll practice this by just crabwalking in circles on the pad at a jogging pace. Looks weird, but it's great for grinding the crabwalk into your muscle memory.
The other tricky bit, for me at least, is the weird center jumps in doubles. LR-RT, LT-RL, et cetera, are hard at first. Again, just gotta practice those until they come naturally.
On my DDR doubles scoresheet (yeah, I make those up for ever DDR mix I have, I'm such a nerd) I have little symbols beside songs that use certain techniques I need to practice. For example, Captain Jack S is good for practicing those center jumps. When I haven't been playing doubles for a while it helps to go back to those for a refresher.
People dance without arrows?