Sewing buttonholes can be a bit scary. First you have to get the buttonhole placements marked on the garment. Getting them evenly spaced can be a nightmare if you don't have the guide that comes with the pattern, or if you don't have one of those handy expandable buttonhole guide things. I don't have one of them, and I don't like math, so I sort of eyeball the spacing and then take a ruler to it to even out the distances between buttonholes. Anyway, my tip is not about spacing your buttonholes...though I'd love to hear how you do them, minus any math involved.
This tip is about marking your buttonholes on your garment....
Normally I just mark a "T" shaped mark for each buttonhole with sewing chalk; the line across the top marking the top where I start the buttonhole and the center line going down being the center of my buttonhole to be. Usually my chalk markings still show on the top, but I never let it bother me too much. They wash out after the first wash.
Yesterday though, I didn't want to get chalk marks on this lovely regency dress I was helping my sister-in-law make, and I had a stoke of genius (at least it felt like one!). To mark the buttonhole placement without marking on the dress, I put down a piece of 1/4 inch quilters tape along the edge of the dress back. All my buttonholes would butt up against the tape to start and thus all be exactly 1/4 inch away from the back edge. I then drew little marks on the tape to space the buttonholes apart evenly and show me where to start sewing them. Afterward, I pulled the tape off, and there were my perfectly spaced buttonholes and no chalk marks!
I'm telling you, this 1/4 inch tape comes in handy for so many things....