In a raid it's typically done like this:
Target the Tank you're MDing to. This can be done via raid frames or direct clicking. Raid frames rock, get used to using them and they will pay back in dividends.
MD has a 30 second duration, or three shots, whichever comes first. The 30 second duration is the key part at this stage.
Cast MD. You get the 'buff', and can see the time remaining with the proper add ons or interface settings.
Type 'f'. The Tank should be targeting the mob he intends to tank. So now you're targeting it also. Fire. Aimed is a decent MD opener if you have it. Auto and Steady do almost the same amount of damage, so either option is fine. Arcane can do decent damage depending on the target.
Triggering BW and/or AP trinkets can help with the rage transferred from those first three shots, so use them if they aren't on cool down.
And that's it.
Condensed:
Target the Tank;
Cast MD;
Type 'f';
Fire.
Edited, Feb 2nd 2008 10:50pm by Kompera