Although this is from my experience of KH250's it may well apply to other machines
1:Removing clutch center nut, first weld a bar to a spare plain plate, put this in the basket to lock it, the nut is guaranteed to be either really tight or already fallen off!!
2:Removing final drive sprocket nut, using a suitable size socket jam it between the teeth of the sprocket and the bottom of the c/cases, opposite side to retighten.
3:To undo the nut on the oil pump end of the crank, pop a 1p or 2p coin between the teeth of the interlocking sprockets, it won't damage the sprockets (after a while you will find a whole load of 'bent' coppers in your garage!!). This only really works where the gears are straight cut.
4:To remove disc retaining bolts, take the wheel to your local tyre fitter and borrow there air impact socket, whizz them off in seconds without damaging heads or snapping bolts.
5:Check your timing more often than you can normally be bothered to, you know it makes sense.
6:ALWAYS position the tang of the kickstart spring before you assemble the crank cases, otherwise the only solution is to split them again, you can tension the kickstart mechanism after assembly by removing the bolt in front of the k/s shaft and 'winding' the kickstart, this bolt will be VERY tight.
BTW IF you break your bike its not my fault!