If you intend on going up then go early to queue for the tickets.
There's a limit of 1320 per day and tickets are often snapped up early in the morning.
Go around 7:30am.
The tip to go around 7.30am is dead right but you should go in a pair and one of you should go for a takeaway coffee and doughnut from San Francisco or Starbucks in Kuala Lumpar city centre to have in the queue. When you finally get your tickets you don't have to take the next available time slot - you can ask for later ones if you want. So, instead of collecting tickets at 8.30am for 11.00am and wondering whether to hang around or not, ask for 4.30pm and have a day out.
Be warned that the visibility from the sky deck can be pretty poor, depending on the humidity and whether it is about to rain, is raining or has just rained. It's still worth the experience though for the ability to wear 70s retro style 3D glasses while watching the Petronas promo film before the trip up!