Paint, will look like..well, paint. Assuming these are haunt walls you don't care about? There are lots of formulas for fake blood. We used the commercial stuff available at Spirit or other Halloween retailers. Pour some into a small pan, dip a brush or even your hand (with a rubber glove) into the stuff and fling it onto the surface. Drips/runs can be acheived by putting some in a spray bottle and squirting it where you want it. Really not hard to get a good effect. Just play with it a bit.
Also depends on your lighting: Low light might need a brighter blood color and bright light the opposite.
There are a million formulas for blood out there, use what looks good for you.
I usually use a darker red paint and throw it all over, make it drip in some spots......Its real messy but fun!
This the effect we obtained last year using commercial fake blood. I forgot to mention that it comes in a spray bottle as well and we got some great effects by standing back from the wall a few feet, squirting it and letting it run down. We got the stuff at Spirit or Party City