Try and keep the thighs nice and loose, especially the lower end near your knees. Once you are happy with the fit, split the difference in the overlap at the backs. Keep the back knee border trim equal and try to keep the curve on the inner halves at the top. You may end up cutting more of the outer top parts at the back than the inner parts but do whatever you need to do and keep them looking as equal as possible.
Post photos of anything you are unsure of and I will be happy to advise.