I�ve built a few wheels and had mixed results. It isn�t rocket science, but it is very time consuming and takes a lot of practice to get a perfectly true result. Trouble is, if you only ever do your own wheels once in a blue moon, you�re sadly never going to get that all important practice!
Truing up a bent rim, as opposed to building a wheel from scratch, is a bit different. If your wheel is out of shape and you fear you might have to get a new rim, or get it seen to professionally and spend some hard-earned cash, I would say it is worth having a go. In my previous dabblings in the dark art of wheel truing (I am by no means experienced or an expert) I�ve discovered that you can rarely make it worse. Nine times out of ten you will noticeably improve the trueness of the wheel. It won�t be perfect, but it�ll be better than before, keep you on the road and you will have started learning a new skill. It does depend on the wheel though; a high quality rim (like an Excel) will be much more flexible than a cheaper one and consequently easier to true. Same with spokes; cheap spokes stretch at different rates (even within the same set) and are difficult to torque evenly, good ones are more consistent. Not sure about the Yamaha rim � I�d guess its on the �cheaper� and more rigid end of the scale! Most people come a cropper by over tightening � spokes aren�t fitted nearly as tight as people think. Let�s face it, what�s the worst that could happen? You might have to take it to a wheel builder, which you would have had to have done in the first place anyway!
Key things to start with are:
Treat your nipples with some anti-seize the day before

.
Get the front wheel off the ground, spin it and mark the out-of-true parts (on both sides) by holding a marker pen or chalk against the fork leg or swingarm as you spin. (Assuming you haven�t got a jig available, which would obviously be the first choice.) Always spin the same direction.
Use a semi-box type spoke tool, not an open-ended one. Work slowly in small amounts, turning spokes no more than 1/8 to 1/4 turn at a time tightening on the opposite side to the mark you�ve made on the rim. Loosening a spoke on one side will have the same effect as tightening on the other. Whatever you do at the out of line part of the rim will effect things 90 degrees either side, and vice-versa. The trick is to pull the bend out, but maintaining the correct and even torque on each spoke.
Spin the wheel and re-mark each time you make an adjustment then you can see the effects of what you�re doing before you start going too far or the wrong way.
BTW � If your wheel bearings are knackered, it�ll all be impossible!
This WBW article is quite a good read:
http://www.webbikeworld.com/motorcycle-wheels/spoke-wheels/
This chap tackles it pretty much the same way as I have done in the past:
Go on, give it a go!