Rain X on goggle lens.
Tape an old goggle lens on the front of your visor, effectively making the visor longer.
I use a couple of strips of duct tape on the top and bottom of each plastic hand guard shield. Effectively making them bigger.
I will run those "glove liner" type thin gloves under my regular gloves. To fight off blisters when your hands get wet. Helps with cold too.
Outerwear pre filter for air filter. It's water proof.
I have a pair of older goggles that have the top foam removed. Really helps with fogging.
I spray WD40 all under the bike's fenders and skid plate. Helps keep mud from sticking, keeping the weight off.
Get in the mental state that you love rainy and cold conditions. You know your competition isn't going to like the conditions. However, you will embrace the opportunity to ride in the nasty stuff, ride with a passion, and overcome adversity. To hell with the rain, you are a dirt biker right? Now go out and bring us home a trophy!
I'll be in my warm and dry garage wrenching on bikes waiting to here how you faired.