Try a stop shot, cue from 1st diamond on one long end, and target at the first diamond from the opposite pocket on that same rail. Place each ball 1/16 - 1/8th from the rail, or step up and have the cue and target touching the rail. The drill is to start first diamond to second diamond, first diamond to third diamond, first diamond to side pocket, etc...etc...
Good luck with that. It's a bitch....makes ya a better pool player though.. :D