Just my $0.02 - as a former menswear salesman.
Get a suit that is mostly natural fiber. Silk is not great - it always looks wrinkled and too casual. Linen is only appropriate for a summer suit. Your best bet is wool or wool blends. Buy a summer weight suit so you can wear it year-round.
The cut of the suit makes it look trendy or dowdy, depending. Look for a cut that suits you and your fashion sense. Darker, neutral colors are best if you’re only going to own one suit. It will not make you look like a fund salesman if you choose the right cut.
Get some shirts and ties at the same time. Do not skimp on the ties - they’re the first thing people notice. I, personally, would not own synthetic ties. It does not pay to economize here after you’ve paid hundreds for a suit. Silk all the way.
Own at least one white shirt, and at least one non-white one. Match them with the ties and suit. Ask for help if you need. A good salesman (or woman) will want you to look good.
IMHO, straight-collar shirts look better than button-down. They’re more stylish and less casual, good for avoiding fund-salesman style.
Make sure the shirts fit, and that you know how to tie your tie. This sounds simple, until you notice how many people don’t really know.
Once you own your suit, wear it. It takes awhile to feel totally natural in it. Experiment a little with the shirts and ties. A suit without a tie looks really good too.
Most shoes do not look good with a suit. Own a pair that looks good with your suit. Have a belt and socks that work with it as well.
If the suit is of a neutral dark color with no pattern, it’s easy to match the jacket with other pants. Get more mileage out of your wardrobe cheaply by doing this.
Clean your suit regularly. Press it before important events. Have the cleaners press it - it looks better and costs very little.
Next week’s lesson will be about the miracle of the blue blazer. Perfect for most of life’s occasions.