Take yourself a US Coast Guard Boating Safety course for starters. Follow their advice on signaling devices especially. With today's cell phones, a 911 call is a super helper. Don't be afraid to seek shelter to ride out a storm. Better to be uncomfortable for a bit rather than be the subject of a missing person's search! At 39mph in a reasonably appointed runabout (type boat) in reasonable water, loaded reasonably you should be in pretty good shape.
#1 is the weather. Never go out without knowing the current conditions and the forecast. If wind is or is forecast to be over 15 mph and you are going to be boating in open water, expect problems with large waves. Always keep 1 eye on the weather when out. If your area has a habit of things like afternoon thunder storms, squalls as they are called where I boated, expect them and when you see one forming, go to safe water and wait them out. They only last for a few minutes but high winds, lightening, torrential rains, and big waves are the norm.
#2 Know your water. Know the bottom contours and especially if you boat in a rocky area where rocks could occur of any size, anywhere that your boat could strike and capsize.
#3 Follow my advice below this reply
#4 Don't take chances. If your common sense and feelings tell you that you may be getting into trouble, listen and take evasive action.
That'll get you started.