Whenever you can pick a project that:
You ‘really’ want to do. Life is too short to waste on something that you are only half interested in.
You think you can do. You have the skillset or you are keen to acquire the skills and experience needed.
You are doing for well thoughts reasons. You should know if you are doing it for money, happiness, personal or professional growth.
You are committed to sticking to in the long haul even when going gets tough. The corollary to this is that it is easier to stick to projects that get you to do what you love as compared to those that you do for prestige or because something is in trend.
Is aligned with your values ie working at that project should not create internal conflicts.
Is aligned with your nature. Your nature may be to work well alone or with a team so the projects should be aligned to how you work, behave and act. This is more important than we realize.
What are you working on?
Is it aligned to your world view, who you are?