Just going to echo what a lot of people have said here, practice, my painting was god awful when I first started now it's pretty good but it's taken a lot of time to get where I am and I know I'm still far from where I want to be. Though I will add two bits of advice, these two things have helped me come along in leaps and bounds.
1. Use flow improver with your paints, it thins down your paints making them easier to blend and it will stop your paintwork looking blotchy, some people use water but I find this leaves your paintwork with a chalky look to it whereas the flow improver doesn't do this
2. If you can find a copy then get the gw 'eavy metal' painting guide. It's no longer in production so check eBay, gumtree etc and as it's a few years old it references the old paint range but if you Google citadel paint conversion chart you should be able to see what new paints replaced the old ones. It's full of helpful tricks of the trade and step by step guides to seriously help your painting.
Keep at it mate, there's few things more satisfying in this hobby than painting a beautiful army and knowing you did it all, having other gamers come up and check out your army during a game then return with their friends to show them too. Good luck my friend