On the misture constistency for fillets. Everyone says "peanut butter" - "add in filler until it holds its own shape" or "until you can't get any more filler to mix in." but until you see that epoxy is sneaky and will run sloooowwwly after you turn your back on it (and only then, devious stuff it is...) you don't truly appreciate the thick consistency needed. For this reason I always put some fumed silica in my mix, thixotropic stuff.