There's a lot of different lateral movements in dressage! You *could* try to memorize exact aids for each movement (which no longer work after your first step), or you could remember the requirements for each, and use whatever aids are necessary to get the job done. (I recommend the second option!)
Below you'll see a chart with each official competition dressage movement. The information you'll need to ride each one:
Direction of bend -- is the horse moving sideways toward the direction he's bent (in other words, going sideways to the left while he's bent left), or opposite the direction he's bent (going sideways to the left while he's bent to the right)? It makes a biomechanical difference!
Degree of bend -- how much bend do you want?
"Ends" going sideways -- does the horse's forehand go sideways (legs crossing), or his hindquarters, or both?