Repeating HG is one of the most difficult challenges you'll face. Very few things can match the feeling of dread that accompanies the decision to try for another child. But many of us have come through many times, so it's absolutely possible!
For me, the most important thing was admitting that I would be sick again. You can waste a lot of precious time and energy trying to convince yourself it's not going to happen again! Preparation falls into a couple categories: medical and personal. Find a good doctor who understands HG and is willing to try new treatments. Actually meet with the doctor and ask some questions, share your history, get to feel comfortable. Draw up a protocol list--a rated progression of what you'll try first, second, so forth. Also have in mind WHEN you'll take the next step in your protocol. Most women start with Unisom/B6, then up to Zofran as nausea increases, then to the next step with vomiting. Just knowing you have more possibilities, more steps to take makes coping easier--you know you're not really at the end of the rope! The second component of preparation is personal. I'd list everything I did all day, every day, and then figure out how those things would get done (or if they needed to) while I was too sick. Working through this before, while I still had energy to think straight, helped tremendously and cut the stress level. Don't be afraid to ask for help--people always said, "If you need anything...", but I was too proud (or sick) to bother asking. Instead, I found it easier when I called right away with a specific task: "Would you be able to help by coming once a week to clean up the kitchen?" Those kinds of pre-prep go a long way when you're in the midst of it.
Other people will have much better ideas--I never got too far on planning before I got surprised with another pregnancy! Good luck to you.