Free hand practice or how to pimp your Briarwood

I bought A-Englands Briarwood ages ago. Bought, admired and forgot for months. I decided it's time to wear this beautiful polish. I wore it on its own for a day, but felt my mani was missing something. Apparently I just cannot wear a polish without nail art anymore :D
Surprisingly, on my nails Briarwood looked more brown then dark red. Nail art with brown?!? Ok, let's practice free-hand painting!

Indoors the golden shimmer and scattered holo particles are very subtle. The magic of this rich deep-red-brown color truly reveals itself in direct sunlight. The problem is, you don't see that much of it in February in Northern Europe... ;)

See what I mean with more red then brown? It looks more dark rosé in a bottle, doesn't it?

I'm still a beginner with acrylic paints. My hand shakes like crazy and when I try to create lines, they are neither thin nor straight ;)  Clear case here: practice free-handing!
I've always liked the delicate swirly pattern on a Bundle Monster BM-314 plate, so I decided to do some swirls on my Brairwood canvas.

I thought maybe a thinner brush would help with finer lines. I cut a small nail art brush as shown in this tutorial and hey! Look at my lines! Almost all of them are thin!!!

Do you have any tips and tricks for free-hand painting?