So, because I haven't bought any new clothes recently (you'll have to wait a few more weeks when I have money for that), and because most of what I have purchased (and will purchase) is of the thrift shop variety I thought I would post a brief guide to how I approach dumpster diving (as my boss calls it) in your local charity/thrift shops. I'm sure there have been many of these written over the years on the internet but... here is my two cents.
1) Thrift Shop Often! Rule one is, I think, the most important. Thrift shopping takes a lot of time input, which is fine if you can't afford to buy quality items brand new. Obviously if you have the time, leave the thrift shops to those poorer sartorialists and students in need. Your local thrift and charity shops change their inventory on a pretty much constant basis as new items are brought in. Many employees of various thrift stores are also interested in quality clothes, meaning they can beat you to the punch BUT, I have noticed that for men many of these fall into the more fashion forward, trendy, edgy, alternative looks. Which means a lot of classic pieces will escape their notice. Depending on the store once a week or so is probably a good rule of thumb here.
2) Go to many shops. As a follow up to going often, go to a lot of different places. We have a few different major thrift or charity shops near me and they their prices and selection are totally different. Some are smaller but are more likely to have great finds for cheap, others have a much larger selection but that means that I have to do a lot more digging.
3) Have a search strategy. This is especially true in the larger shops with more selection. Are you looking primarily for pants or suits today? Odd jackets? Outerwear? Shirts? Whatever your primary focus is, start there. My personal exception is that no matter what I am primarily looking for I almost always start at suits and odd jackets (sport coats and blazers). That is because it is where I am most likely to find a great bargain. Classic designer odd jackets at bargain basement pricing ($5-$15 typically). That is the most bang for your buck since those items new cost hundreds of dollars (or maybe thousands in the case of full designer label suits). Then I will go from there to what I am looking for in particular that day. I may have to put something back later but it is worth having found it first, I can agonize over the decision later when it is in my hand and not someone else's.
4) Vintage stores are great but go to them later. Good vintage stores will generally have less selection than your average thrift shop obviously, but it will be targeted more towards those classic vintage finds you are looking for. But you will pay a premium for someone having done a lot of the thrifting effort for you. Most vintage shops acquire their clothes through a variety of sources but one of them is thrifting. They frequently go to the local thrift and charity shops as well and pick through for the great finds. Beating them to the punch is better for your wallet as long as you have the time to invest. Otherwise you'll pay the mark up. It isn't unusual to see that great $10 Odd Jacket be $40 or more at the vintage shop. That said I do usually drop by when I have a chance because sometimes I find something really worth the mark-up since I missed it at a thrift store.
5) Don't worry about perfect fit, get to know a tailor. A lot of the best finds you'll come across at thrift shops have already been tailored for their previous owner, which means chances are it won't fit you perfectly. Learn how to estimate how much a particular garment can be altered, how difficult that particular alteration is, and how much a tailor will charge for it where you live. Keep in mind that you can almost always resell that garment for at least what you payed for it, if not at a slight mark-up for your efforts on ebay, craigslist, kijiji, or similar so it isn't a big risk often to just go ahead and buy it anyway and worry about the alterations later. Sleeve length is often the easiest alteration to make, as is taking in or letting out the waist of an odd jacket. Then you just need to find a good tailor who can do the work, but you'll have to factor in that cost to your total cost of ownership.
I hope these tips help someone out there. Happy Thrifting!