Buying one of those waterbrushes that Valerie mentioned earlier in this thread was one of the best moves I've ever made! haha. Alexander Grimm also suggested getting them and his paintings are fucking excellent. Takes sooooo much stress out of painting tattooy type images. I just apply paint/ink with a normal brush as usual) and a pentell water brush to blend out. Just start to blend out with the water brush, quickly dab the end of it to get rid of paint that has now come on to it, then blend out some more with it. Real easy. Make sure to only use a smallish sized water brush so not too much water is coming out.
Also, one other thing I noticed don't fill up the water brush fully with water when refilling it. Only fill it around 1/3 of the way maximum. I've found that if it's completely full then the pressure of the water causes too much of it to rush out when you're using it which makes the blends harder to do.
Anyway, hope that helps someone :P
I did this quick rose painting with the water bursh and this longer girl head in a rose one with a water brush too. Definitely saving me a lot of time :)