My best advice is patience. You have to sometimes wait a little while for your stuff to get rare.
Buy as much of the weekend or event specials as you can afford and the forget you have them. They won't be rare for a few months don't make the mistake of trading them too quickly.
The simple act of "trading up" will build your inventory. It can be simple. You have to have a rare item to start. I am going to use a fire window and a rare hat for example and I am NOT saying that these are the values of these things I am giving you an example.
So you have a hat and you trade it for a firewall. You then trade the firewall with someone else for the hat you originally gave plus one other smaller rare item. Then you try to do it again, you trade the same hat for another fire wall or something else and repeat the process. So you are making a "profit" on each trade. It is important to do this with items that you can get and trade over and over. Don't try it with a sparrow or stitch hat or anything that might be difficult to get back.
It can be a little scary at first to trade one rare item that you might like a lot.
I learned how to do that from someone on the boards here when VMK first started she listed all the trades she did in a day and here I was and I couldn't get anyone to trade with me. So I took the one cool thing I had, my costume, took it off and traded it away and then got it back a few trades later.
Also I can't stress this enough, in order to get people to trade with you, read their signatues some people post in there what they want or how they want to trade. If someone wants you to ask first, make sure you do or they will only reject your trade before you even get to show them you rare hat
