If you already know where you will present your results, get familiar with the equipment at your disposition. Know ahead about the projector; what is the image resolution and format ratio? Know about the switches for light, blends, audio (where applicable). If done on-line, get to know this techniques ahead of time, too.
Slightly different to the answer by
@schaedelkeks I suggest you seek a test audience which includes colleagues of your present group who already passed a Master thesis. Not only that they (should) know formal requirements of the talk (e.g., formatting of the slides in general, identification of typos, friendly nitpicking on citing references if necessary). Because of their seniority to you, they may ask questions similar to the ones by a thesis jury after your presentation of the results. Ideally, they should know at least a little about your field you worked in (a.k.a., context), but not too much about your work actually done; otherwise, their lines of thought may be too similar to yours and thus possibly miss errors.
Give at least two test talks. Often, after the first test presentation of a thesis, you work on multiple errors, adjust the argumentation by different sequences of thought, and weed out omissions. There may be this much work that it may be difficult for you to see all the good already brought together. A second test talk thus is more than probing and rehearsing a revised version of your talk. It offers you additional ease when you eventually present your results to the jury.