1. Check if it’s pre-shrunk. Raw Egyptian cotton woven, yarn dyed and finished in Switzerland or Italy is the best by far.
2. Ask about weights of cotton. If you feel the heat, search for lighter weight, or go heavier if you want a warmer shirt.
3. Look at the collar. Make sure it sits well down and has stiffeners that are removable when washing to keep its shape.
4. Mother of pearl buttons rather than plastic, with no brand printed on them, would be my favourite.
5. Smooth poplin cottons look more formal. If you wear your collar open, textures such as Oxford or pique are great.
6. A raised or placket front (the strip of fabric that the buttons are set in) is the traditional Jermyn Street look.
7. Look at button holes as they should be tidy, and with plenty of thread sewing on the buttons, preferably cross-stitched.