If you’re selling your items through any of the online channels, be sure to take great pictures. As potential buyers can’t see your stuff in person, this is the next best thing. Pictures can entice or deter interest. Give yourself the best chance possible and provide fantastic shots.
As for format, it’s nearly always best to isolate items on a plain white background, if possible. That just means putting a white sheet or piece of paper behind them when you take the picture. With larger items, it might be appropriate to shoot them in their intended use (like a kayak in water or a tent set up in the backyard). Whatever you do, pull them out of your cluttered garage and limit as many visual distractions in the image as possible. If you lack the skill or equipment, ask a friend. With today’s high-end phones, someone you know is bound to have a decent camera.
One other thing to consider is light. Properly lighting your gear is essential for a good picture. For indoor shots, I like to use natural light, if possible. All you have to do is put the item next to a window during the day (cloudier days are better). The next best thing is a fluorescent lamp. I like to put it just above and to the side of the item, shining on the front and top faces. For outdoor shots, avoid direct sunlight, if possible. It casts harsh shadows and can show all the imperfections that normally aren’t visible. Just wait for some cloud cover and it will soften the light enough for a good image.