(o•ᴗ•o)

i'd say generally i dont do warmups or exercises unless im really doing a piss poor job of whatever it is im drawing (i only have so much energy so even though its not best practice i must pick my battles). obviously mileage and exercises will help (LINE CONFIDENCE AND ECONOMY ARE VERY IMPORTANT!!! but i cant really tell you how to build confidence beyond just learning your tools, studying primitive shapes and not being afraid to fuck up. it takes time)

i would recommend getting used to changing your brush sizes regularly, my general process at the moment is as follows >smallest size possible for gestural sketch (0.7px on csp) >move up a few sizes (generally 2.5px) while you block in the details >thicker brushes as you move into defining the larger shapes and drawing the eye (thicker linework for things you want the viewer to regard first) generally i go up to 7px then maybe 14px, then i finish off with an outline auto action or do my bold outlines manually

you mostly dont need to fuck around with layers- w this sketching method you can do everything on the one layer ( ppl will ignore verysmall brushstrokes unless theyre extremely messy). same principle with my clean lineart i just skip the gestural step and have the line smoothing cranked up slightly

some thoughts: many artists think you can get line variation thats 'good enough' with a brush thats one size and has a steep pressure curve-- generally i find this creates very wonky looking linework with less obvious intention behind it, and the steep pressure curve makes smooth, consistent lines a bit of a business (obviously ppl can work however they want i just have my aesthetic preferences)