you can drain your radiator and take the lower hose off to help drain some of it and relieve the pressure, but, you almost always still get some coolant in the engine when you take the manifold off, plan on draining the oil before you start it back up after the swap, run it some, then change it again with a new filter ( after getting some water in there plus maybe some gasket pieces it's a good idea anyway).
get some high temp rtv, you should put a skim coat around the water paasages at the front and back of each head, i actually put a skim coat on the head it self around these passages too before i even put the gasket on just because there's usually some pitting around there.
as for the gaskets, not a bad idea to get some high tack gasket adhesive. put that in sveral spots on the heads so the gasket is less likely to slip.
most people just chuck the end seals and use a nice bead of rtv with it dapped good in the corners where the head meets the block..
make sure all the old gasket material is cleaned off the heads. take some paper towels and stuff them in the ports, and maybe lay some down in the lifter valley ( tin foil works good for this too) to help catch the stray pieces of gasket that may fly off when your scraping.
you can use a gasket scraper or a razor blade, when most of it's off you can use maybe some paint thinner or carb cleaner on a rag to make sure they are as clean as possible.....
i'm sure others will have tips for the rest of it....but for the most part, a clean install on the lower manifold is the most crucial part...