OK, so you have your guitar tuned to open D? Before you do anything else, just use your index finger as a Barre and move around the neck. Sounds better? You bet it does! When you are in the majority of Open Tunings, the chord positions that you already know from Standard Tuning, mean very little anymore.
It really is a matter of experimentation, don't forget, you can get some amazing things happening by just using one finger and letting the drone effect of the Open D work its magic.
Start by fretting your 4th string at the 12th Fret and then strum ALL the strings, then try moving your finger either down, or up the same string whilst strumming them all.