This post is based on my own limited experience in selling LadyUmbrella t-shirts in our little spot in the Loft Market in Dublin City. The picture below is how we set up our little patch. I recommend you check out Rotem Wear's post about the same topic as Jean laid out some great points...anyway, without further ado, lets get into it.
Be Identifiable It might sound obvious but if people don't know who to ask or who is working in a shop there is a good chance that the customer will just walk out of the shop instead of risking asking another customer "eh, do you have this in size 14?" or similar. Make sure you are identifiable when working. One thing I do is to walk around the shop with an empty hanger in my hand - straight away people know I work there and have no qualms asking me questions.
Use of FREE People like free things so why not give them something for free? In our shop we have a teapot full of badges and people are allowed to take one for free. This has worked very well (no surprise, people love free stuff) and gets a lot more people over to our section where we can then try sell to them. Even, if they don't buy I think it is good that they leave with a free button which has our web address and logo on it - who knows what may happen in the future.
Lookbook - show off press achievements Another thing I try do in the shop is "show off" our press clippings in a nice book. This, I think, adds more credibility to a brand which will (hopefully) increase a potential customers perception and trust of a brand. It is social proofing a brand to a degree.
Sign You want to try make it as big and memorable as possible. The hope is that people will see your sign above others and be compelled to check out your stuff.
Colour Use as much colour as you can to catch those eyeballs. The more people who see your set up because of the colour the better.
Small Details When you are talking to people try build up a rapport with them as opposed to going for the quick sale. Always be aware of the small details and the nuances of language use so that you might be able to "seal a deal" and get a sale. Use of "just", "only", "today", "limited" and "now" can all help get sales..Not much of a salesman but that is what I've heard hehe...
Room for Manoeuvre This is basically to do with your price..Know what the lowest you can sell your items for so that you can enter into some "bargaining" if needs be to get the sale. People like deals so if you're in a position to give them one give it to them for "today only"...