1. For a 100 story tower, at least 6 express elevators are needed. Make sure they stop at all the basement floors.
2. Build at least 3 elevators from floor 1 to 29, 3 more from 30 to 59, 3 more from 59 to 90, and at least 2 from 91 to 100. Now add extra elevators in high-traffic areas. For example, if you have a 30-floor block of offices, I suggest 4 elevators.
3. Build absolutely nothing except skylobbies on floors 15, 30, 45, 60, 75, and 90. The skylobby must cover the WHOLE floor, otherwise the Sims will get confused when trying to use the express elevators.
4. Always put 8 cars in each elevator shaft.
5. *Useless Fact* Sims waiting on the left side of an elevator want to go up. Sims on the right want to go down.
OTHER TIPS:
1. Contrary to the manual, you do not have to connect your recycling centers to a service elevator- they will still work fine.
2. Build a security station directly above or below every lobby/skylobby, and one in the basement.
3. You only need to build one medical center. Put it on floor B1.