Reviving a deck is an easy D.I.Y. job. When I tackled my deck revival project, the deck was around 10 years old and was looking pretty shabby. Oiling never got a brilliant result despite how much I scrubbed and blasted with the pressure cleaner - it was clear that a full sand back to the bare timber was needed.
I hired a floor sander for the job. They are heavy beasts but surprisingly easy to use. It's a job anyone can do - even those with limited skills like me! I used 40 grit paper for the first sand, then went over again with an 80 grit. It was a big improvement and a project well worth doing. I used Intergrain Ultradeck to oil the timber after sanding and was very pleased with the results.
Preparation is important. Make sure you get all the nail heads down well under the timber surface. Replacing the sanding belts gets expensive and can take a while and you also risk damaging the machine or worse if you hit a nail.
Go with the grain and be really slow and cautious when "dropping" the sander onto the wood. I found it to be the only time you risked sanding unevenly and gouging out a trench. The model I hired didn't have a lever to drop the drum like in the video - this would have been very helpful.
I was (probably very naively) surprised at how quickly the machine wanted to scurry along. You do need to hold it back and go reasonably slowly for an even result. And obviously don't go backwards, always forwards!
Do replace the paper dust collection bag well before its full. If they tear then dust flies everywhere! - Jason
Last time I did my deck I sanded it. Using a pressure washer brings up too many fibres and splinters then you end up sanding it anyway. - redracer01
If you are not planning on sanding the deck, then I would highly recommend you use Intergrain 4L UltraPrep Timber Cleaner first if the deck has patchy colour to it. If you do sand you most likely will not have to use the cleaner.
Here's a D.I.Y. guide on How To Sand A Deck, which you can see how they achieve a uniform colouring with fresh timber before proceeding.
If you manage to do some preparation but get interrupted by weather, needing to wait a few days will be fine. Try to keep any leaf litter off it in the meantime, if wet leaves sit on the deck they might leave stains. I would try to avoid washing it again with water prior to oiling/staining your deck. If the wood is saturated with water it won't absorb the coating very well. It would be preferable to apply the coating to a dry deck, that way it will soak the oil/stain deep into the timber.
If you are trying to go from a darker stain to a lighter colour, it would just about require the complete removal of the current stain. This can either be done via sanding the whole deck or attempting to use a paint stripper. Using a paint stripper is messy, time-consuming and will be quite expensive given the amount of product you'll probably need to use.
The other option in that situation - instead of attempting to reverse the stain now is to wait until it is due for a re-coat in approximately a year and a half. By that stage, it will have lightened considerably and you could then apply a natural oil with no stain included.
These step-by-step D.I.Y. tutorials might also be helpful: