Things to consider:
Budget- What can you afford. If you can afford new then why not new.
Fit- Maybe the most important thing to consider is getting a frame that fits your anatomy.
Components: Vary in performance and weight according to price. I advise not geeting components so old whereas repair parts are hard to come by or hard to match up.
Name brands: There are many good frames and even more opinions on which is best.
What kind of riding am I doing: Touring, racing, mountain biking, etc. You may start out on a mountain bike and end up on a road race frame but I suggest making a educated guess on what you will be doing for the next year.
It is always a good idea to look to a reptuable bike shop for advise.