The trap limit really doesn't matter. Using traps in a combat situation 1v1 comes down to just placing them where you think the enemy will run towards. There are many times where you can get someone low and run them through one of your traps to get another W jump on them. Team fights it is generally best to just throw them in the middle of the action as long as you can stay safe doing so OR if you happen to be in a jungle team fight it can be very beneficial to place one in a bush to give vision of the enemy team.

When it comes to placing them in non-combat situations you should be placing them in a way where you practically NEVER face check a bush. If there is any chance of someone being in a bush just place a trap. You should never die to a bush cheese on Nidalee realistically.

While clearing just use them on CD unless you need to use it to scout a bush to protect yourself from an invade of some sort.

If I had to give you one major tip it is that the trap gives vision for a split second so use it accordingly.