What I do is (starting with the innermost layer): tuck my t-shirt under my underpants so it doesn't come loose. Tie the drawstring of the pants like Cherie said through the little loop, the knot it with half a shoestring tie, that is, I make a loop on one side only, that way the knot is somewhat more secure but I can still pull it open after practice (and yes mine gets sweaty and difficult to undo). I've sewn extra ties on all my jackets, and then after a couple years had them ripped off all but one jacket, haven't bothered to put them back...my obi goes around my waist because that is the only place it will stay. Make sure you know how to make a proper knot on the obi, ask one of the seniors.
And when I'm not wearing a hakama, I will be adjusting my jacket all class long, but if you look around, so is everybody else. It gives a welcome little breather every now and then.
kvaak
Pauliina