Along with objective placement knowing if you want to go first or second is a key factor to winning games. Usually this is determined by your army and the army you are facing! Building a knowledge of knowing what turn your opponent wants can benefit you as well, giving you the opportunity to mess with there plans. Of course, a little knowledge can be a dangerous thing.
After loosing the roll off and being passed first turn, it was time to spring a new plan on him using the infiltrate ability of my Genestealers. I put out my two broods of Stealers in terrain in opposite central positions, walking on my Hormagaunts into terrain on my turn one.
Here in the picture below you can see my Daemon opponent having to think long and hard about how to deploy? I pretty much had it covered so that no matter where he came down I was ready to munch him...
Although we should all be planning our tactical game around what turn we want to get. Don't forget you always need a back up plan for when it doesn't go your way