Before You Touch the Cover

Pump standing water off the cover firstIt's important to drain your pool cover to prevent melted snow or rainwater from getting into your pool.
Skim leaves and debris off the cover before lifting itSo nothing dumps into the water as you pull it off.
Hose the cover down and let it dry fully before folding it awayIt'll mildew in storage otherwise.

Get the Water Moving Again

Top off the water level with a garden hoseFill until it's about halfway up the skimmer opening.
Pull the winter plugs and reinstall return fittings and skimmer basketsRemove all the plugs or Gizzmos installed in your pool returns and skimmers, and replace return fittings and skimmer baskets. Water can't circulate with those still in.
Reinstall the pump, filter, and ladder/railsUse fresh Teflon tape and silicone lube on o-rings and drain plugs.
Prime the pump before you flip it onOpen all the valves before and after the pump, and open the air bleeder on top of the filter. Prime your pump by opening the lid and filling with water. Running it dry can burn out the motor.
Run the filter system continuously for the first 24 hoursGets the water circulating and clear.

Test the water before adding anythingGuessing at chemical doses on a holiday timeline is how you end up with cloudy or unswimmable water right when you need it clear.
Adjust total alkalinity first, then pHTotal alkalinity should be between 80 and 120 parts per million, and pH between 7.4 and 7.6.
Shock the pool with chlorine, then let the filter run 24 hours before anyone swimsWith a holiday crowd adding more bather load than usual, you want the sanitizer level solid going in, not catching up after.
Add chlorine stabilizer (CYA) if saltwater or unstabilized chlorineIf you have a saltwater pool or use unstabilized chlorine, you need to add a chlorine stabilizer. CYA should be between 30 and 50 parts per million.
Add calcium hardness increaser if the water tests soft if water tests softMainly a concern for plaster or vinyl surfaces.
Retest the morning of the party, not just after shockingExtra sun and bathers shift the numbers fast.

Check the gate latches and fence self-closers workA pool full of relatives' kids is not the weekend to discover a gate doesn't latch.
Check that drain covers are intact, not cracked or missingDamaged or non-compliant covers are an entrapment hazard that's been the subject of repeated federal recalls and warnings.
Keep a reaching pole and life ring in plain sight near the pool before guests arriveCheap insurance that's useless if you remember it after someone's already in the water.
Assign one sober adult as the "water watcher" whenever kids are swimmingWith a crowd, it's easy for everyone to assume someone else is watching — name the person out loud.
Skim and vacuum the pool surface the morning ofSo it looks (and tests) its best when guests show up.