When first starting out, giving back to the community (forums) and providing help to people for everything from web design to web hosting issues, this will earn you quite a bit of respect and often times will transfer into clients.
For us, we have strong ties with particular software. We've been the largest X-Cart hosting provider since they started in 2000, and with more than 5,000 posts in their forums providing troubleshooting and assistance, we have a nice little niche in there. We have more than 2,500 X-Cart ECommerce customers as a result.
One of the biggest places you can put your money however is directly into SEO. Do a search on google some day with just "cpanel hosting" and have a look who is in the #2-4 position... oh, that's us
How does a little guy like us beat a giant like Hostgator that sells the same product? SEO baby! Instead of paying for advertising on the google adwords, we dump it all into SEO and we get the traffic as a result. Just that phrase alone gets over 60,000 searches per month. Many of the phrases we go after are getting anywhere between 15,000-300,000 searches per month, and we're ranking position 1-5 on them. Any phrases less than 1,000 searches, we nearly always take the #1 spot on Google & Bing.
So, from our end, if you're spending money on Adwords, spend it on SEO instead. It will take a few months to get results, but it will last much longer than the money spend on Adwords!
Team up with web designers and like minded individuals. Cross promote products. Purchase banners & graphics on various blogs and forums. And always keep in mind who your target is - end users. We normally stay away from advertising where other hosts are advertising - less competition means more reward.