Adding to what 4c6 said, look for something that you think can be improved. Ask around, see what problems folks have with the status quo- scheduling, check lists, streamlining procedures, training- or come up with something you feel needs to be addressed, and provide a possible solution. Unfortunately, just doing your job better than everyone else does not always translate into opportunities for advancement. You need to be proactive and and promote yourself- nobody else will do that for you. Add to your skill set- take every extra course, seminar you can.
Here's the thing- you need to figure out exactly what your goal is- to move up in the company- which may mean no longer working the streets, become a supervisor, trainer, or start taking management/office/leadership classes to position yourself for that route. The more tools you have at your disposal and the more hats you can wear, the more attractive and valuable you will become to the company.
Find a way to save the company money- that will almost ALWAYS score points with management.
LIke you said, be careful to not step on any toes. Couch your proposals carefully as to not offend, simply provide a better way or even another option. Make sure you are seen as trying to help the company- and yourself, not just trying to stir the pot.
Lastly, give it some time- you also need to get more experience, but there is no reason why you cannot start planning for the future now, so when your time comes, you will be ready to move up.
Good luck.