When I was younger, I got my first taste of the 41st millennium at my local hobby shop when I read a copy of the old Daemon Hunters codex. Remember that one? I can't find a copy of the picture to post here, but you should hopefully know. The horror and disgust that filled my mind enthralled me, and I was irrecoverably hooked.
About decade later, I bought my first Space Marines from a friend; I assembled them and left them be, too scared to paint them in case I messed up. I decided on a Chapter name, heraldry and everything and after six or eight months finally decided to buy some paint.
Two years have passed since then. I still have my first squad I painted, and as much as I want to strip them and thus absolve myself, I need to keep them to remind me just how far I've come. I've compiled a few photographs of my Astartes from then to now. Sometimes I felt so useless with the brush I wanted to just throw in the trowel and give up painting, but I remembered that old codex, remembered why I started the hobby and took heart, picked my brush back up and carried on.
Oh, that sounded lame. Never mind. Picture time.
Second squad-- I sort of had an idea where I was going. I had already proposed to hand-paint the icons onto the shoulder guards, but I was still very poor. Watering down dryad bark was something I thought of, but was too scared to try it.
I found out about writing script on with pencil; also, what started as an accident became my signature of sorts-- the white stipple.
Third squad-- my Chapter was only going to ever have two devastator squads, so I wanted to do my very best. Dryad Bark left the yellow a nice, dull ochre, so I was very happy; I also found using watered down Bestial brown left a nice, rusty finish, along with a bit of Fire Dragon Bright drybrushed over.
Fourth squad-- by this time, my confidence had grown along with my repertoire of techniques. I started using a pitt pen more often, including make-up around the Astartes' eyes. I also found that colouring the basing sand orange and drybrushing it with Zandri dust as opposed to dabbing the paint on all thick, it made a much nicer base overall.
Fifth squad-- throwing any and all caution to the winds, I tried splotching watered down Caliban green and Abbadon Black over the brown before the rust wash. The result was a very bitter, dark colour that I felt befitted the 41st millennium quite well.
Sixth squad-- but I didn't stop developing my skill. After acquiring some technical paints, I went to town with oxodising brass, sticky, caked-on blood and decades worth of grime. I also found dropping a little watered down Nurgling green into the eye worked better than trying to highlight it with a brush.
This is my most recent Astartes. I always strive to paint at least a little like the John Blanche, and I think I might be getting there.
So you see what two years of painting can do for you. Just keep practicing, don't hold back with new ideas/techniques, and above all things, let the Emperor guide your hand as you paint.