Not black or brown, not beige/cream. Light grey or navy blue are the best imo, but no banker pinstripes! Get a nice, tailored or slim fit one, but most importantly one that fits well, so try plenty on. On the highstreet, probably Next or Zara for around £100-200 suits. You can try tk maxx for branded ones at similar prices but I’ve never seen a particularly nice suit in my tk maxx, or one in a good fit. Topman and river isalnd have okish cut suits, but the quality is so so. M&S suits, i find, are quite a blockish cut, and never really do justice to anyone.
Simple rules such as a shirt that is lighter than the suit, with a tie darker than the shirt, make any suit look good (avoid the “i work in IT” look, which is wearing a black shirt with a suit…)