One thing to keep in mind, IMHO, is to avoid falling into some of the traps that the SCA heralds complain about. Such as working in overly-modern charges (such as ice cream cones), or getting carried away with an overly complex design. There's what's referred to as "resumé heraldry", where people try to fit in a large number of charges at once (such as "well, I'm a blacksmith so I want an anvil, and I fight so I want a sword, and I was born during a full moon so I need a moon on there").
I'm guilty of the latter to a certain extent. I had 3 main charges I wanted to use, though I considered designs with only one or two of them before settling on what I'm using now.
But what a symbol means to you might differ from their historical heraldic meaning, so that's another angle to approach it from if you're lacking in ideas. You can start with a meaning and pick an animal or object to use accordingly.
But also keep in mind that whatever you come up with, you may wish to paint into shields or stitch onto fabric. Animals are hard to do. Multiple animals makes that harder. Though of course, stencils can be an option here to make that a lot easier.
Historically, particularly in the earlier parts of the period, heraldry was often more geometric with maybe only one or two charges.
Take a look at the Dering Roll of Arms (circa 1270-1280) below:
