It's scary the first time if you've never worked an attic before, but before long you'll be fine.
First, you don't need boards, although if you're up there for an extended amount of time in a given location installing a celing fan box or something, they might be helpful.
If you have a well insulated home, take a wood handled broom with ya to sweep the insulation away, and also to put it back when yer done.
I also find Rubber knee protectors quite handy, and essential if there isn't enough room to stand (watch out for roofing nails protruding from the roof decking!).
Just stay on the rafters, and travel in a direction perpendicular to the rafters. Hands and knees... the rafter spacing you might find is conveniently such that your knee can be on one rafter, and the top of your foot will be alongside the one behind it, and your hands in front of ya, and you can crawl quite comfortably without freaking out. Standing, just keep your feet on separate rafters and keep a hand on something and you'll feel quite secure, and get the hang of it assuming you have no medical problems with balance. If you're on your hands and knees, it becomes pretty darned hard to fall through a ceiling unless you're under 16" tall.
By all means be careful, but it's really not that bad. You just have to get yer "attic legs" and stop thinking so much about there not being any weight bearing surface between the rafters.
Best Regards,
-- Todd H.