Please check Traction book, there are 19 channels you can use. Brainstorm ideas first of all on each of channels, write down ideas. Then evaluate what is the cost of implementation, what is potential reachable size of market for this idea or channel, what can be conversion. Based on these assumptions choose 3 best ideas and test them.
After you run tests, measure and afterwards adopt ideas or choose others if these didn't work..
Dont forget it is repeatable process, iterate, iterate, iterate. On different stages of startup different ideas and channels will work