This is how I was trained to draw/paint:
-Start by observing your subject (the betta in this case). Look at it and try to notice shapes and lines you hadn't before.
-ALWAYS draw from observation, instead of from memory. It makes a difference.
- Do many quick, loose sketches of your subject, 1 or 2 mins tops. They will be bad, but do a lot of them so you start to get a feel for the shapes. Try drawing many different views/positions of the subject.
-When you go to do a longer drawing, spend more time looking at your subject (or photo) than you do looking at your actual drawing. This seems weird, but it forces you to observe your subject more closely and see things you usually don't notice.
-PRACTICE. Your first drawings will be horrible. Everyone's are. The more you draw, however, the better you will get.
I hope this helps!