As a first-time investor the choice of shares available can be quite daunting. So it's important to research companies thoroughly. Be wary of tips, particularly from brokers who have a vested interest in getting you to part with your money. It's very important to know your market, and a good exercise is to play the market virtually at first. Pick out some shares after some research, and monitor them over a period of time, working out how much you would have made in profit, or lost, if you'd really invested. Watch for what happens to make the share price increase or decrease.
Decide what kind of company you want to invest in. Do you have any specialist knowledge of particular companies and how they work? This gives you an added advantage and makes research easier. Check out your chosen company for management structure, future plans etc.
It's a good idea to look at a company's Annual Report and it's accounts. If you look at two years worth of these, you can see if future plans have been followed through with and whether these were successful. Look for companies with a good track record and consistent performance rather than one that fluctuates regularly.