If you have a winter cover, remove it. For solid covers pump the water from the cover, underneath the cover, back into the pool. Add water to proper level.
Connect filter and pump. Turn on pump. For d.e. filters open air bleed knob on filter until water shoots out. Close air bleed. Add recommended amount of d.e. filter powder slowly into the skimmer. Check pressure gauge. When pressure gauge is 10 lbs. Over clean running pressure the filter needs to be cleaned.
Clean the filter block, the skimmer and return, with plugs. Open the drain plug on the filter and drain filter tank. Take off the filter cover and remove grids/fingers/or cartridge, depending on the model of d.e. filter you have. Rinse grids/fingers/cartridge thoroughly. Remove pump cover and clean pump basket. Make sure to lubricate any O-rings with silicone lubricant only. Vaseline will ruin O-rings. Put filter back together and re-install the drain plug. Remove the plugs from the skimmer and return. Open air bleed and turn on pump. When water shoots out close the air bleed. Add recommended amount of d.e filter powder. Filter until pool is clear. Have water tested and balance as soon as possible.