increase quality

HI,

Now I'm finally able to print, after a lot of weeks it's working.
My first prints have not a good quality, I want to increase this. Actually I'm printing PLA with layer 0,2mm, 210°C, print speed 40mm/s and flow 120. I think, this are the main features for quality?Is there any rule of thumb, what I have to change, when I increase or decrease i.e. print speed (flow up or down, which values for +/- 5mm/s?) or anything else?

Please help.

I didn't find the right solution from the Internet.

References:
https://tevo-3d-printers.com/viewtopic.php?t=340
Business video agency

Thanks!