General method.
1. go to http://www.sbstransit.com.sg and
click on "Journey Planner".
2. Key in your starting location and ending location which in
your case will be "Ayer Rajah Crescent".
3. Follow the instructions and out will pop out a suggested
route.
Specific answer.
If Starhub is still at 2D Ayer Rajah Crescent, take 91 from
Buona Vista MRT same side as MOE building, get off for Ayer Rajah
Bus Park and ask for directions from there. You'll have to walk a
bit.