Digital rendering and brushes for beginners

[Tank Rat]

Thanks for the advise! I tried editing the brush settings, but the result still didn't feel great. I did find a few brushes I liked. I did a lot of blending exercises to get a feel for what felt good to use. I also did a few primitive studies (I'm doing 1 a day this week). 

It easy to fill a form using a lasso but the result tend to look flat in my opinion due to the edge quality

Your definitely right about that. You'll really be able to see that in these primitives I'm posting below. It's very apparent in the sphere, but a bit less so in the two cubes (really tried to soften those extremely sharp edges). Again, thanks for taking the time to offer me some advice.