I know how to sew the most basic stuff, like fixing a hole in a pants pocket or stitching a button back onto an old shirt. Knowing how to do this is handy.
But I liberally take my clothes to one of the local seamstresses: Mary or Anna. A lot of my clothes have gotten new life that way. Six dollars here, 10 bucks there. Highlight: an expensive down jacket had a ruined zipper. For $12 I got a new, sturdy, bronze-colored replacement.
I've also been wanting to see if Anna can do some mods: combine two old sweaters, etc., add elbow patches, etc.