1. Each whitelisted project awards the same amount of GRC under the magnitude system. This means that projects with less crunchers reward more, as your crunching will represent a bigger portion of that project's total magnitude.
2. Pick projects with lower competition from other crunchers. The Gridcoinstats projects page can help with this
3. Pick projects to match your hardware. If you are crunching with CPU, it will be hard to compete against GPU crunchers for projects that support GPU.
4. Math and physics/astrophysics projects tend to have less competition than health and medical research projects.
5. Keep in mind the efficiency of your hardware. For projects which support GPU, they are often many times more efficient than CPU. Likewise, newer hardware tends to be more efficient than older hardware.
6. You can use a third-party tool like FindTheMag to identify the most efficient projects based on your hardware's performance. These tools are not produced or endorsed by Gridcoin and require you to crunch a bit for each project before being able to produce useful stats.