as per what dean says.
if the recess has rust or debris in it.. scrape clean. clean both surfaces.
shouldn't need any sealer on the gasket.
if your mating surfaces are excessively rough and or pitted, go ahead and hit with a wire brush / sand paper to knock off anything loose and shine it up.. then use some permatex #2 on the gasket/flange and assemble and let cure up a bit before adding water.
same on the hose connections. go ahead and wire wheel the nips for the hose. many times they are excesively pitted. i've seen some pitted enough that wore a water line down the side that would not seal with a new hose and 2 clamps. in those cases you can repalce.. or go the buba way ;) and rub some rtv ( i like black ) on it.. less is better than more.. don't want it IN the cooling system. then slip that new hose onthere and clamp. should actually make it easier to put the hose on too.
post back if you hit a snag.
ps.. make sure your thermostat ain't warped from trying to install incorrectly..