The boat should be prepared for its photo session. Remove all extraneous gear laying around the boat. Tidy up any lines. Arrange the seats. Check the position of the outboard engine. Make the boat as presentable as possible. There is no reason to take a candid picture of your boat when it is sitting on its trailer or tied to a dock. You have plenty of time to prepare the boat for photography.
Wait for good lighting conditions. Do not take pictures with the sun backlighting the boat and in the frame, unless you intentionally want to create a silhouette of the boat. Low sun angles just after sunrise or just before sun set are often the best lighting conditions. Take advantage of them. Try shooting at different exposure settings, trying under-exposing and over-exposing by one f-stop. This can often result in enhancement of the image quality. Of course, be sure to be in focus on the boat, not the background or a foreground object. Boats are usually longer than they are tall, so do not orient the camera for a portrait layout. Users of the iPhone and other rectangular smartphones, please take note of this. You are driving the rest of us crazy by shooting everything with the camera oriented 90-degrees from horizontal.
Vary the perspective on the boat. Some boat hulls look rather odd when viewed at certain angles; those hulls have particular sides or views that look much better. Try to use those angles.
Take more than one picture, changing the composition slightly or moving the camera position. It can be hard to see exactly what is in the view of the camera with a small viewfinder, and you may discover something distracting later that you overlooked. Take a lot of images. Then pick the best one.
Don't be afraid to crop the image. Not every scene has composition that fits perfectly into the pre-set aspect ratio of your camera's image sensor. Crop out extraneous material.
If you have skill with an image editor, you can also try various exposure compensation or color corrections. These generally require some skill and taste, so use them judiciously.
Here is an image of my boat that I took several years ago. I had to walk about a quarter-mile around the marina docks to get this perspective. I waited until the setting sun was just about to go below the tree line. The lighting was very good at this moment. The boat was reasonably tidy, although I see a couple of items I could have hidden. The framing of the boat in the overall image is good. The lower right part of the frame is a good location to direct the viewer's eye. In this image, that is where the Evinrude E-TEC engine is positioned. Although I took this image for my own use, it so happened that Evinrude saw the image and asked if they could use it in one of their in-house publications. I was quite honored to have my boat featured in their dealer magazine--on the cover!

The Boston Whaler boat CONTINUOUSWAVE at the seawall of the marina in Northport, Michigan.