How do I effectively rub spices into fish? I did a fish rub for the first time last night. I mixed the spices and then put the thawed tilapia fillets right into the bowl. I noticed two problems:


The spices tended to clump up and became difficult to work with.
After cooking I noticed that there were some VERY concentrated pockets of flavor; not at all uniform. Sometimes these were unpleasantly strong.


Any advice for next time?
First of all, if you're seasoning tilapia, you'll want to add some oil to it, since tilapia has almost no fat.  So, here's the steps:


Drizzle oil over the tilapia (both sides).
Sprinkle it lightly with the spice mixture, all over
Let sit 10-15 minutes.
Sprinkle with starch (e.g. flour) at this point if you're frying them.


Optionally, you can also add some lemon or lime juice (just a little) in step 1.  You also want the tilapia sitting on something flat, with the filets in one layer, like a large plate or baking sheet, not heaped up in a bowl.

For spicing small filets, you want a finely ground, moderate-flavor spice mixture.  Unlike beef or pork, you're not marinating the fish for a long time, and you're not cooking it for  along time.  So the spicing on the fish isn't really a "rub"; it's spicing to eat.  I recommend against using rubs designed for meat on light fish like tilapia.