1. The width of the tie should match the width of the lapel.
2. In general, thin lapels are more modern. Wide lapels are more old-school, Mad Men style.
So choose your look accordingly.
3. A pocket square adds an extra level of polish, but make sure it doesn't match your tie in either pattern or fabric choice.
4. When buying an off-the-rack suit, the number one thing to check is how the shoulders fit.
5. A collar gap between your jacket’s lapels and your shirt’s collar can signify an ill-fitting jacket.
It's complicated. Read more about it here.
6. Opt for a charcoal or gray suit over black, unless you're attending a funeral.
7. Your belt should be fairly thin and the same color as your shoes.
8. You should match your shoes to the color of your suit using this guide:
9. Double vents in the back are more modern and fashionable.
This look is also more flattering for larger figures, and it gives you enough room to do that effortlessly casual "hand in pocket" thing.