Deadhead the spent flowers by pinching the flower stem at the base and snapping it off, no pruning required unless you need to improve the shape of your shrub. Mulch well with something organic (will cool roots, condition soil, conserve moisture) and give it regular water. If the foliage is a pretty color, and you don't see symptoms of anything eating the leaves, no more is required.

We're cool in summer here and I water with drip hoses, deeply, once each week that it hasn't rained. If your soil is sandy or very fast draining rather than the amended clay base soil I have, you might even find you need to water more often if your summers get quite warm.

Organic mulch - anything that once was a live plant. So compost or composted steer manure (plants that have been diverted through a digestive track), both available by the bag and not expensive at the box stores like Home Depot. You can shred leaves with the mower in Fall and add those to your garden, some people mulch with pine straw. I don't care for bark chips, and bagged mushroom compost is the wrong PH for rhododendrons.

Just spread it out 2 - 3" deep over the root zone, which will extend out a little farther than the longest branches. You can even toss it with your hands, if the steer manure is well composted it should be odor free and dry (and the product at Home Depot for $0.98 has been). I mulch all my beds, perennials and shrubs, with compost each Spring, some I make but due to limited space for a large composting set up, I buy my share too.

Buds for the next seasons flowers are set in late summer. If yours were damaged, there isn't anything you can do to encourage more to form now for next Springs blooms.