Step #1: Establish a total budget. Realize that most vintage bikes have been ignored/neglected for many years, so part of the budget will need to go to refurbishing the bike. If you have the time/tools/aptitude, this can result in getting a great bargain. A really nice, totally refurbished bike might sell for $250, while the same bike in neglected shape could go for $50. But if you have to pay someone to do the work, it will rarely make sense to buy a project (a bike shop could charge you $250 just for the rehab and parts!!!). In that case, look for a good/great flipper in your area, one that will do all of the work for you, at a steep discount to any bike shop. And a good/great flipper should have several bikes on hand, so you should be able to test ride them for fit, etc.

Step #2: Figure out your sizing. Spend time on google "bicycle sizing", and study up. Then test out a few bikes on what you think will be your size to verify. Also study up on how bike sizing is determined. Many/most sellers have no idea what size bike they are selling, and seemingly can't use a tape measure.

Step #3: Create a target list of what you are looking for: several brands, several models. Then you are ready to pounce when one of those bikes hits your radar screen. I look for features and construction, and don't care much about a specific brand or model. The more open you are to various brands, the quicker you will find your bike. I only have one bike where I targeted an exact model and year. It took me three years to find it (and I look for bikes every day), and it was 2,000 miles away.

Step #4: The best deals are at garage sales, thrift stores, church sales, and from neighbors. The best deals on Craigs List are the ones with no pictures, no size, little or no description, etc. The best deals on ebay are local pickup only. If you are looking for a great deal on C/L, don't expect the seller to provide good pics and accurate details, instead, just go look at it. A lazy seller often = a good deal.

Study the pictures of finished projects routinely posted on this forum. You will quickly learn what a good bike looks like, versus a project. Most of the "catch of the day" pics are projects. Occasionally people post after pics as well.

Don't worry about making a mistake!! Buy right, and even if you change your mind later, you will be able to get your money out of the bike and move on to the next one. I routinely change out my "keeper" bikes. Been doing it for the last several years. But I am getting dialed in, so maybe I'll keep the current ones for a while.