If you help people, and help them well, then your actions and attitude will promote themselves.
I hate self promoting, but I've been successful gaining a reputation as a competent, helpful, senior team member in a number of companies by simply helping people and making friends with them.
This advice obviously won't be applicable everywhere (I've never worked in a company that used stack ranking for example), but I've worked in start ups and enterprises and I've found that people respond really well to someone who ignores the office politics and existing team rivalries and just helps out when something needs doing.
In my current (enterprise) environment I've used that attitude to get an openly hostile lead of another team on to our side (and now consider him a friend outside of work as well), and two of my managers (one replaced the other) have both commented on it. I've also had people from other teams who I don't know and have never actually talked to recommend me as a good person to ask advice from, so I can only assume that it is noticed and spread further than my immediate team or the teams I've directly helped.
It's worth pointing out that you'll need to put your own team first - no one's going to like or promote a teammate who neglects their work in favour of other teams, but your team will also notice and appreciate it if you're a person who brings support from others when they need it.