Bleach breaks down organics (critters and algae)and helps flush them off/out of the rock. Acid removes phosphate by dissolving the outer layer of rock. Bleach and acid have to be done separately if you want to do both. Bleach first, acid second.
You could probably skip the bleach process and just scrub or powerwash the rocks seeing as any critters or algae are probably quite damaged from being dry for so long, but the bleach wouldn't hurt. 10:1 freshwater to bleach is plenty. Rinse well then air dry for a few days with a fan on it or use a dechlorinator (you will go through a big bottle so air dry is prob best).
For an acid bath, make sure all bleach is neutralized first or you will end up with dangerous chlorine gas. Rinse the rock thoroughly after the acid, and baking soda will neutralize the remaining acid. Do rinse well first or you will be going through a ton of baking soda.
Afterwards, test pH in the tub after it has been circulating for a few hours and pH 7 or 8 (depending what your freshwater is) indicates the acid is neutralized.
If it was me, I would do the whole she-bang. I don't like skipping steps when setting up a new tank because it just creates headaches later. Do it thoroughly now, and save yourself grief later. If you don't want to do all this process, you can toss the rock in the tank, let it circulate for a week, do a 100% waterchange and repeat as many times as you're willing (the goal is to lower nitrate and phosphate by leeching it out of the rock). This process is slower, but less physical.
Have fun!
