I love full head weaves for hair growth! I live in what I consider a super sized steam room, so I haven't had one recently...However, when I did, I would engage in a full on "hair spa" prior to hiding my hair away.
I shampoo, protein (I usually do a light protein, as heavy proteins require too much work to return the balance back to my hair), deep condition (like I am about to go to visit an old friend in hell and don't want the flames to sear my tresses), regular condition and moisturize (I always air dry).
For moisture, it is done over 1- 2 days. I usually rinse out my conditioner, then spray with the Aveeno liquid leave in (My hair must be wet, and I run my fingers down the length of it to smooth the cuticle). I then get some creamy leave in, apply that, and seal with something heavier (and less slippery) than an oil. I put my hair in plaits, and take them down the next day to check to see how they 'feel'. Depending on a variety of things (whether I have been diving/swimming/drinking sufficient water/out in the sun all day/sleeping well/wearing my hair loose prior to the spa) I may need to add more moisture, or co-wash and use something different.
I also second (third or whatever number I am!) other who say don't let them braid too tight. Also, I always use a net (even though people often think it is only for those that have problem areas) to distribute the weight and stress evenly. I also always have the stylist use additional hair to braid mine (even though mine is long enough), but the skill level of the stylist might dictate whether you want to do this (if they aren't good, it could look bulky).
Hope you like the outcome when you get it!!
Once you get something you like, you will really enjoy the style!!