Generally speaking it's a good idea to check whether or not the broker you want to work with is licensed and regulated by a respected regulator, like the British FCA. Check whether the regulator has issued any warnings about them, as the FCA often does. Then check whether people, ordinary people I mean, have left any reviews about that broker online. Check what their terms and conditions are in detail. If you are satisfied with what you've seen, open a demo account with them, trade on it for a bit, call them a few times to determine what their customer service is like. If you are still pleased with them, open a live account and invest a small sum of money - small enough that you can afford to lose it - then soon after withdraw it to observe what their withdrawal process is like. If you are still satisfied you've likely found a broker you can trust.