Quick tip: V-necks are AMAZING!! They perfectly mirror the inverted triangle and draw the eye inwards and downwards to your waist. Plus they're so versatile if you get some good quality ones!
I'd say avoid cap and puff sleeves. To me, cap sleeves look disproportionate and almost like you're wearing a shirt that's too small in the shoulders. Puff sleeves emphasize the shoulder line purposefully, so naturally it's something to steer clear from (no matter how cute I know, I'm bummed too).
Really the main rule of thumb is balance. I found that now that I have a clearer idea of my body type (yay, inverted triangle/hourglasses!), I can visualize how something will appear on me, which makes online shopping easier. Just be aware of your strong shoulder line and take note of details up in that area that draw the eye there; things to be wary of include epaulettes and boat necks. But hey, everyone's proportions are different, so there are no hard rules! If you love say, that puffy sleeved blazer or that safari shirt so much, go ahead and try it on and see for yourself. Everything's meant to be a guideline. If you break a couple of rules and you look amazing, no one's going to be bothered.
