If I were you, I would invest in some Citadel washes. They are IMHO the best shades on the market. The washes are easier to work with than inks because they are much more forgiving to new painter mistakes. They pop out details with minimal effort. I recommend the following colors: Agrax Earthshade, Rekland Flesh, and Nuln Oil. You can add colors based on your pallet but these cover most situations when starting out. I actually only use the famous Nuln Oil on silver metals and grey colors. It's black and really overly darkens other colors.
I know a lot of people love the Army Painter "tone" washes but I have never used them and cannot speak to their effectiveness. I have used Vallejo washes and hate them but I do love Vallejo inks.