I know one thing, for sure. If you dad is a mountain climber he has to stop in squamihs for a day. World renowned climbing there.
Ok be prepared for pretty groomed runs. I don't know your level but most serious expert and pro levels downhillers find whistler fast, flowy and not technical enough (I am talking pros and experts DOWNHILLERS, most average trail riders come here and get put in their place, xc racers get wrecked and beaten and freeriders learn what freeriding is) Whistler is meant to progress. In one day you can go from 1 ft drops to 10 ft depending on how much you put into it. The trails are well labelled and all of them offer something different. If you are used to these trails (as in mountains) start on blues. Keep in mind there is a large range of blues. Good started line is b-line -> ho chi min (this one will really tell you if you are ready for some of the blacks) -> heart of darkness. B-line is rated a green but you can fly down this trail at mach 4 and really work on berm turns and little jumps.
If your addiction is air try b-line to get a feel for speed and then move to a-line. Fast, flowy and lots of jumps. Rumour has it a baby a-line will be installed next year which will help because some of the faces of the jumps are damn intimidating. Avoid this trail during busy times, if you can't keep up people will yell at you. Also Dirt Merchant. My favorite air trail. Steps up and step downs and big jumps. Bring your balls for this one. I found it easier than a-line but more intimidating as well. There is also crabapple hits. 4 LARGE and LONG Jumps. I ride this one, but don't air it. The speed needed to even get up the trannies is more than a-line haha
Another good blue is fantastic. Kind of rutted but fast with BIG berms and some tiny step downs. This brings you to the play zone with jumps and drops. Play in there to get a feel for the steep trannies whistler users.
Next move to golden triangle. Now split into to the 1st section has some steep rocks, if you aren't used to it, you may freak yourself out. You can then challenge yourself to the last part of duffman which used to be blue but is now black, for a reason. Stay wet most of the time, kind of steep and if you miss the last turn you could tumble 10ft. Either that or go straight and stay on golden triangle.
If this was easy move to angry pirate, which imo is one jump or steep part away from black. This gets you really warmed up for garbonzo. Steep, tech, short tight turns, log skinny BUT FUN!. My favorite trail on the mountain by far. From here you can hop onto a-line or whistler single track.
Now move to blacks. Imo Whistler Lower DH is a good start. Steep downs, drops and 4 steep rock faces. This is a fast flowy traditional style dh course with some good tech stuff in it. My worst crash happened here when I rolled a rock face to a right hand berm but forgot to turn.
If you can do this one move onto upper whistler dh, schleyer. Then past that national dh and joyride. You will also find garbonzo relatively normal but keep in mind Garb is traditional pnw. STEEP, Rooty, Technical and mostly wet. Bring your A-game
If you want stunts start on the 2 play areas and then move to Heart of darkness. Big wide but flowy boardwalks that get you used to riding in the trees. Then move to Clownshoes which is a decent trail but I don't much like the baby step downs they put in mid skinny. Not my style.
In the valley, there are three trails everyone should hit. River runs through it for awesome flowy north shore. This will really show you what flow is like and why no one does the shore better than shore builders. If a stunt is there it was put there for a reason, not just for fun. Kill me Thrill me is an awesome trek. Go up through many switch backs and then come down. One of the classics in whistler. Needs to be experienced so you can really say I rode a whistler trail. And thirdly, get into the valley an explore. There are djs, trails, shore trails all over. Whistler mountain is pretty tame compared to some of the stuff in the valley.
The biggest thing. Learn to brake, or better yet WHEN to brake. Whistler kills newbies coming up here. they come up for 7 days and ride 3 because there hands can't keep up. Braking constantly causes pain. Learn to module and release. From Top (gabonzo) to bottom you can be on one solid dh trail for 30 minutes. From mid point 10 to 20 minutes depending on skill and the trail (on a-line fast riders do it in5 minutes...trust me, thats nuts) Get those hands used to constant aching somehow, workout brake all the time.
You should also hit the shore once. It is an experience and really nothing like it in the world. Heck even walk it. The easiest trails are blues and blacks for most riders. Think of it as an experience and not a ride.