I am quite a successful active investor (sorry for the lack of modesty).

What I look for is:

1. Small companies (none of the serious big guys look at small companies so you have a chance);

2. and are doing some real and valuable;

3. and are being ignored because the past management were terrible, but where the current management has nothing to do with the old management (reverse takeover, backdoor listings, etc).

On point 3 I am amazed how many investors treat companies like people. They will continue to punish a company for the sins of the past even when everyone involved is different.