Photography is another hobby of mine, I have decent cameras and I still have issues taking good photos of my drawings. I'm used to taking photos of stuff and things, not drawings in a sketchbook. Good lighting, and keeping the camera level and square is a challenge. If the camera isn't square with the drawing you will get keystoning, creating a trapizoid rather than square / rectangular. From the camera end of things It is easier to photograph the drawing vertically hanging on a wall rather than flat on a table. Unfortunately flat on a table is generally going to be far more convenient from the work piece side. Angled on an easel probably the most difficult due to frame of reference of the camera. A flash can create many issues, uneven light, hot spots, reflections etc. Good even light will almost always provide a better photo. A couple of clamp on worklights can be a cheap and effective method of lighting your subject. Take note of the light color used, daylight, soft white, fluorescent etc as that will make it easier to set the white balance in the camera,

If you're having trouble taking evenly lit photos with interior lighting sources take your sketchbook outside on a sunny day and try to snap a few pictures in the direct sunlight, or in nice evenly shaded area. As long as it's even, and you don't cast a shadow directly on the work with your phone, you should have an easier time of getting an evenly lit shot of your sketches. Hope this helps!

I saw a reply from Marshall V at some point and place, and he basically said to have 2 different (yet equal) light sources pointing toward center of paper to illuminate it evenly. Something another student shared with me that has really helped, is to use the GRID option (if taking pics with a phone); it helps to ensure everything is level and square. Good luck!