Never do anything that can be considered spam. If you do it hurts all hubbers. You can add a link to a hub on Yahoo Answers for example, but only if it's relevant and only after you have thoroughly answered the question asked. Sites like that are not intended for hub promotions.
Get active on social media and get a following. Promote your own hubs, but also promote other things that are interesting. No one is going to follow you if you just push your own stuff all the time. Actually participate in online forums and communities, develop your own site or blog, do anything but Spam people, it's not just you you're hurting if you do that and it won't work anyway.
Pinterest is a fun way to promote hubs. Give your hubs a Pinterest friendly graphic and pin them. Again, only do this if you are pinning other things too so that you don't look like a spammer.
It is very important to never cross that fine line into over promotion, it will backfire.