My dude, my suggestion is also start off with some quality shoes. For me, I'm not 100% at where I want to be, my body is still changing while I'm losing a couple more kilo's. But I started off with shoes, because I knew my feet wouldn't change. I have a nice pair of chinos that I bought a few months ago, and suddenly they're slipping off my waist
but
That's just a suggestion, if you're beginning to work out and your body is changing.
However, if you're comfortable with your size, Ksteezy has some good advice already posted. Also look for the right fitted shirts. I think Calvin Klein had one or two nice dress shirts, I can't remember the name of their fit, but I had a couple white ones, and they were shaped nicely for me. Also work on your tie game. The shirt can make a HUGE difference when you have tied the tie perfectly.
I believe, start making subtle changes...they'll have a big impact in the long run.