First, Some cleaning and stripping solution and a few tools. A scrub brush, bucket, safety glasses and don’t forget sunscreen!
See if any wood is rotten. NO cleaning can bring damaged wood back that needs replacing. Then, scrape off the old finish on the railing and decking. If you have an OLD finish that is really worn out, and looks uneven consider a solid color stain to make the wood look consistent and even. And if this is a two day job, remember that strippers, cleaners and stains DON’T LIKE hot dry days! Instead it should be cool and overcast.
You’ll need to do this every couple of years!