When you're just starting, I think it's helpful to make a chart of different mixtures of your paints like in the pic I posted.
As far as medium goes I'd mix one part thinner and one part linseed oil. Use it relatively sparingly, I normally just dip my brush in it and then dip that same brush into whatever paint I'm using and mix it around a bit.
Buy some acrylic gesso (golden brand is the best, but store brands like blick or alt alternatives are fine too) and coat watercolor paper, cardboard, masonite, practically whatever with it a few times and you have yourself a solid painting surface. You can also sand the surface down a bit if you want a smoother surface to work on.
I'd also recommend going to the hardware store and having them cut you a 1/4" pieces of glass at 18"x 24". Put some white foam core underneath it and duct tape the edges and you have yourself a great palette. Much cheaper in the long term than those shitty pieces of palette paper too.
When you're just starting, take it slow, enjoy mixing the paint, getting a feel for what colors do what. Try to break down complex forms into simple shapes, and then ask yourself what color those shapes are. I'd look at some Euan Uglow, Fairfield Porter, or Felicia Forte to see how they break down what they're seeing.
Most of all keep painting, but also keep trying, but also be sure you're practicing and not just mindlessly pumping out paintings.