Not very many people can hold onto two homes at the same time, so you will need to sell the one you have at present.
Here is a quick overview:
Buyer's and seller's markets: When there are alot of people looking for homes but not many for sale, this is called a seller's market. When there are alot of homes for sale and not many people buying them, this is a buyer's market.
Wait for the market to improve? : If you are selling one home and buying another, you don't really have to worry about playing the market. If you sell your existing home for a low price, you are probably also buying at a low price.
Seasonality : Do home sales get frostbite? It's true. Winter sales tend to be slower, and spring sales tend to be more brisk.
If you need to sell fast: Ask a Realtor for help establishing a price and how to make your home look attractive, without making you look desperate.
Buy first or sell first? : Many people are able to time their sale and purchase so they happen on the same "closing date". As a buyer, you can make your offer "conditional" on the sale of your existing home, so you are not paying for the upkeep of two homes. Or when selling, you can try to extend the "closing period" to give yourself more time to find your next home.
Sell with a Realtor, or on your own? : In the same way that many people decide not to fix their own cars or do thjeir own dental work, it is wise to enlist a professional when selling your most valuable asset. Real estate transactions are complex, time consuming and involve a lot of legal documentation. Your Realtor is knowledgeable and highly motivated to help you get the most for your home.