How do I write about the New Deal and it's effectiveness?

The most important thing for these questions is a clear and relevant application of what you know, what basically adds up to being a clear structure and clear line of argument. What do you mean by "effectiveness"? Did the New Deal result in a radically changed society free of racism and a perfect welfare system - no - did it result in net positive changes and change the shape of government - yes. Decide what the terms in the question mean first, it'll make your line of argument clearer.
So firstly decide what opinion you agree with and say which historiographical school that lines up with - did the New Deal fail and suppress radicalism? If you think so you're a New Leftist, if you think it was broadly positive with some wide ranging changes, you're a Leuchtenburg revisionist. Then lay out what the rest of your essay is going to talk about clearly, "while figures from the New Left such as Howard Zinn and Barton Bernstein may believe that the New Deal was a conservative attempt to save capitalism, I disagree for the following reasons".
It's important that you've planned stuff out here, so take 5-7 minutes of your 45 to nearly hammer out in your head 3 things to talk about.1) Roosevelt, intellectually, was not as radical as a figure like John Dewey or Henry E. Sigerist who asked for a greater expansion of government than Roosevelt did sure - but he was still at his core helpful.2) The New Deal did actually help people - big federal works plans between 1935 and 1943 employed 8.5 million people and created structures like the Triborough bridge. 30 million people were covered under the social security act of 1935. The FERA employed rural rehabilitation programs and granted funds to colleges and unis to employ students part time.3) Changed the structure of government forever, making central government a lot stronger, and more interventionist. Republican Wendell Wilkie campaigned on these grounds in 1940.
Paragraphs should be written in the normal, Point, Evidence, Explain format and in the conclusion you should just be giving a clear and succint version of what you've already said in your wider essay - if it looks like a repeat of your intro a little bit - don't worry.