Since the seals are very tight, a simple trick to help get in the thing is to put a plastic grocery bag over your hand/foot to push through the seal. I wouldn't recommend putting one over your head unless you are going for the Darwin awards. Under the suit I generally wear thin PJ pants and a long sleeve shirt.
Also, be sure to pee before you put it on and if you are going to fart, be sure to vent the air out a sleeve. If you fart and forget, venting out the neck can be a horrible situation. Trust me.