Unless you have a good artistic reason not to, when you snap a picture of your bike (or anything else, for that matter), try to keep the horizon line, well, horizontal.
Most of the times, a photo with a slanted horizon line tells something like "amateur photographer in a rush"
instead of "good photographer who takes time to align his camera"
Most newer cameras (phones included) have an option to display guidelines on the viewfinder. Use it and try to align your horizon every time you snap a picture. You'll notice the difference yourself.
Compare the two photographs below. One is well aligned with the horizon, the other is not. The difference may be subtle but the effect on the viewer can be significant.
INCORRECT: Slanted horizon line
The horizon line is slightly slanted on this photograph, making the clouds look unnatural. The scenery is beautiful but something just doesn't feel OK.
CORRECT: Horizontal horizon line
The photograph below is well aligned with the horizon, that makes the clouds and everything else feel more natural and it's easier for your brain to feel comfortable with the image.
What if I can't see the horizon?
With perspectives, buildings and mountains, sometimes it's hard to SEE the real horizon. When that happens, try to visualize in your mind where it would be if those buildings/mountains weren't there and align your camera to that imaginary horizon.
I hope this simple tip helps you take better looking photographs :)