Surely the best way to search for a broker is to start from an accurate research. Look for the best reviews, see if there are any customer complaints and details of each broker. Don't be afraid to try brokers' demos, most of them are free, so you don't have to commit to just one platform right away.
But surely the things you need to pay more attention to are:
Transparency
A broker must simply and clearly communicate commissions and anything else they may charge you. A broker who tries to hide this information is to be avoided.
Regulation
There are several major regulatory bodies in charge of supervising brokers, such as CySEC and FCA among the best known. At the bottom of each broker's page you should find the regulation numbers.
Transparency and regulatory oversight are just two of the many factors to consider when selecting a broker.