This is the same quandry I'm in, after writing a number of novels and making them available as e-books on my own site. Just like your case, my novels are science fiction, so they are competing with a horde of other material. How to rise above the hordes? I'm still working on it, and always looking for opportunities to shine.
Right now, a double-sided "passive" approach, participating in SF-related forums (like this one), and hosting a professional-looking website, get me some recognition and sales, but certainly not much (I still have my day job!). And my budget is limited, so I can't, say, spring for multi-thousand-dollar ad space in a major magazine or website.
So I'm trying to identify smaller, more targeted (and significantly less expensive) venues for advertising... in this case, SF magazines, and any SF convention that accepts advertising for its programs. Even if you can't get a magazine to review you, an ad might attract as many eyes. There may also be SF-themed websites that you can advertise on, if the rates aren't too high.