OK
Purchase quality bearings with the suffix 2RS (NTN,SKF,NSK,Koyo etc)
Remove one seal from the bearing. Pickup new seals as well.
(There are numbers on the bearings and seals and they are usually less $$
at a bearing shop)
Completely clean the wheel , axle etc .
Pack wheel , bearings with new high quality grease.Assemble
Hope this helps!
note: bearinsg with one seal run cooler and add less friction the 2RS bearings.
Personally , I use Bearings with one Z (less friction again) . ex 6204 Z
The outside seals are the most important to keeping dirt out.
hope this helps