I'm storing spices and dried herbs, as I always did, in glass containers into a spice only-drawer. It always worked fine.  But looks that this house is particularly humid, because ground spices, and even seeds like fennel, started to become moldy, and they're not THAT old... I don't always have access to new spices, so I must buy them all around once in a year. Is there amy storage  tip for avoiding mold? 
Hello from the humid Philippines! I'll answer regarding the amount you keep in the jar out of storage.   I completely agree with the idea of vacuum-sealing any excess spice. That's what I do, because I can only buy certain spices (brown cardamom, sumac, etc) in bulk. I use a desiccant in my spice jars, which have rubber gaskets for an air-tight seal.   If you go to your local hardware store, you should be able to find screen material made out of plastic. Cut some to fit the bottom of your spice jar exactly, put some sushi rice (basmati also works if you can't find the really fat variety) and then put the screen on top of it. Then, put in your spice of choice.  The rice is enough to draw out any humidity you introduce into the jar each time you open it, so your spices stay fresh and are much less likely to clump together.  If you can't find non-reactive screen material, some cheesecloth will work. You can also just mix the rice into the spice (not recommended as rice is starchy, and the spice will clump around the grains as they absorb moisture).  