What I noticed that affects price the most in the coins I've seen so far.

Short run:
- a marketing team that talks about the coin, although in some cases people start believing or are invested enough in what is sold that it becomes a long run price raise.
- famous people or organisations that are (or are rumoured to be connected to the coin, e.g. the basketball player that did a trip for potcoin or recently a famous poker player that got into the casinocoin board)
- anticipation for the certain release of a feature (more often than not, price rises high in anticipation before that, then it just drops like a brick, no matter if the feature is good)

Long run:
- following the roadmap, delivering on time often affects the price in the long run.
- technical innovation (if it is actually marketed) on a feature that is hot atm. E.g. the privacy craze a few months back, but only the coins that were marketed (e.g. deep onion had quite some bounties for mentioning the coin on the forums or putting it in your signature).
- and finally, real-life usage is the only thing that seems to keep the price stable or make it rise in the long run.