Hi. I am a novice when it comes to miniature painting technique. To get a grip with learning to paint in fine lines, I decided to use a Turkish tile design. The practice worked well and I was able to see my own mistakes while developing fluency. It would be nice to know what other techniques are good to practice.
There are broadly 2 types of lines... the Turkish style seems more broadly to incorporate a variety of 'strengths' within the lines, ie thick and thin lines, meaning that there is variation within the same line - it starts thin, gets thick towards the middle then thins down again towards the end. And this gives a very beautiful, dancing effect. The other type is more broadly a classical Persian style which is absolutely uniform lines, so no variation at all inside the line. (This is talking about outlining, not rendering; and if you get into Chinese painting there are whole books written about the various numerous different line styles!) In practise you find both in miniature painting and there is no boundary, it's quite blurry.
I would say, looking at your red flower heads, that in general you render according to the form, not perpendicularly to it as you have. So you would render along the lines of the edge of the tulip, lengthwise, not 90 degrees to its edges.
You can dive into the world of tazhip/tezhib illumination to practise those different types of 'dancing' lines, and there are brush exercises for miniature painters too (straight lines, spirals etc and just doodling. I love doodling, eg on the phone!).