Like James says, 2 halyards tied
to the harness or bosun's chair. I use an ATN Mastclimber and it's a relatively easy trip up and down. The mastclimber is a solo setup so the second person is essentially there to run the winch on the backup halyard. Tie off a bag for tools - where possible I tie a securing string to tools so they don't go down w/o me. Ascend with an extra line in case you need to pass anything up or down to crew on deck. I need to wear fingerless gloves but that may be due to the way the mastclimber works as you're climbing a static line. Try to do it on a calm and cloudy day and ask those on deck not to dance around - small movements below result in larger swings aloft. As mentioned, inspect the rigging as you go - ascending and decending as you're eye will catch different things. Have some rigging tape handy for any boots or radar reflectors. Bring a camera up so you can inspect pictures later and the novelty of getting a couple of shots from the masthead.
I'm about 190lbs and go up our 28' double spreader rig.