I've been riding my longboard as a means of transportation for 3 years. While riding 20 miles or more a week (through New York City) it was important for my bearings to be clean. Here I show the most efficient way I have found to clean bearings.
You will need:
1. Box cutter/sharp knife
2. Brake parts cleaner/degreaser
3. Ball bearing grease, 3 in 1, Sewing machine oil
4. Small flathead screwdriver
Step 1: Remove Shields From Bearings
After you pop out your bearings from the wheels, you must remove the shields to access the ball bearings inside. This can be done by using anything with a sharp pointy tip like a box cutter. Stick the tip into the inner ring and pull up.
Step 2: Cleaning
After you have removed the shield it is time to clean. The best is to use a degreaser with a long spray nozzle to blow out the dirt and grease. Place the bearings in a cup and blast away
Step 3: Greasing
This part might be a little controversial but after using all types of oils (3-1, Teflon coating) I have found that grease actually works better. It's a matter of opinion but through trial and error this is what I have found. Using a small flathead screwdriver, get little clumps of grease and put it into the bearing coating the top. The free spin is much much much slower but when you get out on the road it makes a difference. You may also use any type of oil you'd like.
Step 4: Finish
Pop the shields back on and go riding!