In my opinion there are a few things keep in mind (and this is a "do as I say, not what I do" kinda thing-I waffle like crazy

):
-In writing succinctly, you need to know what you want to say. In terms of essay lingo, this means having a clear, structured plan in your head, on how to tackle the prompt, and what you want to argue/discuss. Often when people just respond to a prompt head first, before considering the prompt's implications, and what the assessor wants from you, they tend to waffle, and as a result, they end up with a longwinded essay, and an ambiguous contention/argument. So tl;dr: have a clear idea in your mind what you want to say.
-Another tip is to have an idea on how you want to say what you want to say. Usually this step would be pretty easy once you know what your argument/message is. If you are doing poetry, then consider which poems would best substantiate what you want to say. If you are doing a novel/play, consider appropriate quotes. Your means of conveying ideas should be taken into account, if you really want to write as tight as possible. And at this stage (assuming you're in year 11), I wouldn't worry about time constraints; just really work on writing better and better.
-The final thing I wanted to add was to reread past essays you have written, and pick up any phrases or sentences that either digress from your main point, or don't add anything new. For example, in your topic, in most (if not all) cases, 'clearly' and 'succinctly' really convey the same thing. Of course there are nuances (imo succinctly also implies saying something short and to the point, while a 'clearly' written essay could be quite long, although it would be hard to do-and not recommended), but the main thing to say is that often when rereading what you have written, you can pick up on parts of paragraphs that don't really improve what you want to say. If you still need help with this, perhaps post an essay up and I'll try have a look, see what I can do (no guarantees my feedback will hope, but the offer is there

).