But of course you should always do what you enjoy most. And most of the following points happen automatically over time anyways.
- Specialize in rigging. The more time you spend on other disciplines, the less time you will have spent on rigging. Note: Of course it is good to have a basic understanding of all connected areas, to improve working with the different co-workers (modelers, animators, r&d, pipeline) and to be more independent, require less feedback and be able to give better feedback. But after the basics there will be a moment, when it is better to do more rigging instead.
- Work closely with animators as soon as possible. Because they are the people that use your rigs?! If you are an animator yourself, this is not as important. But there are also different preferences between animators.
- Work with experienced/specialized co-workers. Because animators will know what they want and if they have a lot of experience with different rigs, they will request the nicest features they know and improve your rigs that way. Good modelers will ease/improve deformation. And generally the better the co-workers the better the end-result, which will make your work look better. And you can learn more from each other.
- Work on few projects (quality>quantity) with people that work on few projects. If everyone has more time the quality of everyone's work should be better. Also the shorter the length of the film the better the quality (animation, rendering,..).
- Create few character rigs (quality>quantity). Try to find projects with few characters (or do not rig all of them if there are too many). To improve quality and because you can only show a few rig demos in your demoreel. Note: It is also important to learn how to improve pipeline/workflow/speed. If you have to rig a lot of characters you are forced to do that, but you can still do it with a few characters if you want to.
- Rig extreme (cartoony/realistic) characters. That way you learn how to create extreme motion (2D style) and recreate anatomy (deformation focus) in CG. If your character is stylized in-between you don't learn as much about anatomy, because it is not required (same for extreme motion). It basically is about having a good/clear target to aim for. Note: Some people probably want to focus on either cartoony or realism, so the other area can be dropped. That way the quality should improve in your area, but it will reduce the amount of companies you can apply to.
- Rig different kinds of characters/creatures: Biped, quadruped, bird, snake, mechanical, ... Because they have different requirements and anatomy.
- Scripting: Learn to script, to automate repetitive tasks. Optional: It can also be good to learn programming to: 1. Write better scripts, that other people can work with 2. to create new tools for other people to improve workflow 3. Write plug-ins for new functionality 4. Design a pipeline... These things are usually done by more experienced professionals. For a student it probably is better to keep it limited (see point 1.).