You can save your slides as a Show, rather than as a Presentation. It's a simple option in "save as" under "save as type," just as if you wanted to save it as a PDF instead. If you save something as a Show, then as soon as you click on the file, it will open up your first slide in full screen all ready to start presenting, rather than opening it in edit mode.
A couple of caveats.
1. If you think you might go back to edit it again, make sure you SAVE CHANGES in the Presentation version before you save as a Show. You actually CAN edit a Show version, but it's harder to get it to open in edit mode (you have to do it within PowerPoint, rather than in Explorer or directly from a desktop/file folder). So I find it easier to work with the Presentation version, but save the Show version for the actual presentation.
2. If it's something where I'm going right into the material without a title (like my presentation tonight for HDFS Follies), then I like to have a blank slide at the beginning, so that I can open it up as early as I want but don't have to show my first slide until I'm ready.
“The post PowerPoint trick #2: Save as a show first appeared on Eva Lefkowitz’s blog on May 2, 2014.”