I had my surgery less than 2 months after I decided to call a surgeon and find out the process. I'm in Australia, and the insurance regime is way less intense than in other places. We don't even have to lose any weight to get approved. There's no waiting. I think if I had had longer to prepare, I would have gotten more and more nervous!
My preparation suggestions:
have a plan - who are your support people? tell them what you need from them. Decide if you're telling your colleagues, friends, strangers, heck if you're going to snap chat your surgery - whatever. Figure these things out.
take lots of "before" photos and measurements (I wish I had done this).
write a clear list of reasons why you are doing this (this was helpful to me, I keep it on my phone and look at it when things are difficult). You might make a dream board. It's nice to have something visual.
if you know people who have had surgery, talk to them to get their perspectives. If not, then check out forums, youtubers, blogs, whatever. You will feel less alone. I even binge watched a lot of My 600lb Life and documentaries on weight loss surgeries.
educate yourself on what a high protein diet looks like.
read and learn all the information that your surgeon and nutritionist will be providing you. My family also read this information. Ask your surgeon if you have any questions.
think about what you want to pack for the hospital. it doesn't really matter what you bring, but if you feel prepared and in control, it can help.
think about your kitchen. Are you OK with other household members keeping bad food around? i purged my pantry and keep all junk far away from me. people who live with me have to keep the chips and crap out of my sight!
Consider if any mindfulness techniques will help you. Relax, read, light a candle. Indulge in crappy reality TV. Make a playlist of songs that help you feel calm. Whatever is soothing. You need to learn how to keep yourself happy without food.
If appropriate, get therapy.
start your vitamins NOW. these will help your body heal after the surgery. I think vitamin D is particularly important.
If you can, start some light exercise like walking every day. Being fitter will help you cope with the surgery and your new life.
start drinking lots of water.
acknowledge and appreciate that your life is going to change. Make peace with it.