The OP asked specifically about a new job in accounting. Well, I have some experience there having previously worked at PwC for three years (as a tax lawyer, not an accountant) before jumping back to BigLaw.
Some of this may sound outrageous (as in, basic common sense) but unless you've been there, you can't even begin to imagine the horror of what some accountants wear. I worked with a senior manager in the M&A group that wore fleece zip vests every single day! And not nice fleece (if there is such a thing) but horrible moss coloured pieces of garbage.
When I was at PwC I wore suits every day and caught a lot of flak for it. I wore the suits because that was what I had from when I worked at a law firm. Let me say that at accounting firms things are much more casual. That being said, you can still look good. Just remember: fit is everything.
My advice is as follows:
1) Buy a blue suit. No pinstripes. Not fashionable (i.e., no skinny lapels or Thom Browne short jacket). This will be your go to suit for all important client meetings, etc. You will probably wear this suit 10 times a year, if that. Buy something in a classic fit that is not too baggy or billowy (accountants love comfortable clothes).
2) Buy a pair or black, lace-up, cap-toe oxfords or bluchers. Buy shoe trees. These will be the shoes you wear with your suit. You will probably not wear these every day.
3) Khakis. These will likely be your everyday workwear pants along with office pants. Do not buy pleated pants. I repeat, do not buy pleated pants. Flat front, slim, but not skin-tight. Buy several pairs in different shades. Recommended brands are Howard Yount or Brooks Brothers.
4) Office pants. Again, flat front. Do not buy pin-striped office pants. Glen-plaid are ok, but solid colours are preferred. Grey, charcoal, navy blue, and dark brown are the preferred colours. Flannel is your friend. Charcoal flannels are the best thing you can wear. You won't stand out, but you'll look better than anyone else.
5) Shirts. This is the easiest thing to screw up and ruin. If you will buy shirts that are too baggy on you, you will look fat and slovenly. You do not have a suit jacket to hide the excess fabric. I recommend using Mytailor, moderntailor, justwhiteshirts.com or any other e-retailer with low prices for MTM shirts that are tailored to fit you. If you want an example of how shirts should fit do a search for Phat Guido and look at his shirts. Buying OTR you will pay too much for shirts. Go internet MTM. Start with one shirt at a time. This is advice I wish I had when I was 21. As for colours, go with white OCBD, blue (but not too many!), tattersall, and gingham checks for spring and summer. Button cuffs, not french cuffs.
6) Ties. Buy 3 ties. One dark navy, one sky blue, and one "other" colour. You will likely never wear them other than with your suit.
7) Everyday shoes. Buy a pair of black or dark, dark brown leather-soled dress shoes. It doesn't matter whether they are bluchers, brogues, oxfords, or wingtips. Just do not buy rubber-soled, square-toe slip-ons. Polish your shoes. If you do this you will probably look better than the managing partner.
8) Jeans. Most accounting firms are "casual" on Fridays. I saw people wear things that I would wear if I was washing the car. The memories haunt me still. My advice, work from home on Fridays.
9) You don't need pocket squares for your suit. If your wear one, you will be the only one wearing one. White cotton is best. Expect abuse. Don't compain. You asked for it.
10) Do not wear anything other than a white undershirt under your dress shirts. An undershirt is not the same as a t-shirt. Undershirts are meant to be worn as undershirts. I saw people wear brown or red printed t-shirts under OBCD dress shirts. Please do not do this.
Many people will have different advice based on their own experience. The foregoing suggestions were based on my three years at PwC and are worth exactly what you paid for them: nothing. That being said, you will notice a number of people dressing exactly as I described. Try not be be like them.