how can I sew my trousers so that they fit?

hmmm your description here not too precise. theres many factors that effect the fit on a garment, and unless your a proffesional tailor i wouldnt advise you taking matters in your own hands.
but here goes, if your bum isnt fitting, i would advice in buying a pair of pants that do fit your rear. then taking in the waist around. and tappering if needed. that way you'll avoid the need to affect the original visible stitching of the garment and all the work can be carried invisibly.
otherwise take it to my drycleaners.
173 york way london camden n7 9ln

shan kurrim
May 2005