Welcome!

Others may have some suggestions but I found this tutorial by Christopher to be really helpful. It's on alternate picking but I feel it really gives you good string awareness. Something else that I have been doing lately is another string awareness exercise I found... Pick the first string, then the second, then the 1st, then 3rd, 1st then 4th, 1st then 5th, 1st then 6th. And then go back....6th and 1, 5 and 1, 4 and 1, 3 and 1, 2 and 1... It takes a lot of practice and excercises like this to get a good feel for where the strings are in my opinion. I'm a little rusty right now so I've been working on this too. But practice, practice, practice...you'll really see improvement with some basic exercises. :D

Have fun Remco, and again, welcome. This is a great place to be.