I happen to be planning for a Bulge 44 campaign game right now. My recommendations:
1. Start with smaller sceanarios that are pieces of the general campaign, and play these through to the end. That will give you some insight into the capabilities of the units, the axis of advance, supply considerations, etc.
2. Make sure you carefully review your side's OOB, but not necessariy the other side. You should have a good memory of the general OOB.
3. Create maps and plan the route of advance or the defence. Once you have a plan stick to it, unless the situiation changes. I was playing the Peiper scenario (i.e., working my way up), and I did not plan. I found that I waffled in my objectives, and units were therefore muddling around on the battle field.
4. Keep notes on a move-by-move basis. Normally your planning maps should be your guideline, but from time-to-time, you may have a specific task for a unit. For example, if you know you want to move a bridging engineer to a certain hex, record it. In my Peiper game I lept forgetting where I wanted to move specific units.
5. Read books on the campaign.
6. Understand what it takes to win the game (objective hexes, how many units to destroy, etc.)
7. Make sure you and your opponent understand the commitment to the game. I happen to have an opponent who is OK with one turn per week, or even slower. We joked that we hope they have wifi at the retirement home. Other players won't be happy unless you give them a move per day (I wish I had the time). It's a committment, so get to work!