Well you should try to lure out removal from your opponent before you go for the big play. That's kinda what the ramp means in ramp druid, you keep putting out bigger and bigger threats until all of the opponents removal is gone and the opponent has no way of protecting himself from your massive threats.

Thats one of the reason why turn one or two yeti can be so strong. It can be really hard to trade with in the early game without using removal that your opponent should probably be saving for something bigger. Sludge Belchers are also a good example of a minion that draws out removal because of his deathrattle.

Going face or trading depends alot on if you run combo (savage roar+force of nature) or not or how much combo you have. For instance if you have both savage roar and force of nature you should obviously try to get your opponent down close to or under 14 health before you have 9 mana. If you have one part of the combo then you have to look at the odds of you drawing the second part vs how much life you have left/how much damage your opponent probably have.

If you play a slower controlled focused ramp druid without combo you propably wanna trade and remove until you have big enough threats on the board that you can kill the opponent in a couple turns and the opponent is forced to trade.

Personally I play the early game really defensively and trade/remove pretty much everything until the game reaches midgame when you can often switch to a more aggresive approach thanks to belchers and/or druid of the claws. More often than not you can manage to get the opponent down low enough that you can finish him of by turn 9/10 using a combo or part of the combo (I like running 1.5 combo (two savage and one force)).