I use two step ladders to dry my inflatable kayak. I space the two ladders a metre or so apart and drape the deflated boat over them.
It's important not to do this in your living room immediately after getting in - drain out any excess water outdoors first!
You will have read in your kayak's manual about the importance of rinsing, thoroughly drying and properly storing your inflatable kayak. And you'll probably remember from your own experience the trauma of getting your tent out for a trip, having stored it for a full year, but when you open it out, it's filled with mould and mildew and stinks. Not good.
Why does this happen? Because you were too lazy to dry it properly, and just packed it away on the field and put it in your closed. Well, that's what happened to me anyway.
And the same can happen with your kayak - at least you don't have to sleep in the yak.
The problem is that after a long day on the water you might just want to pack up and get off home or to your next destination.
The thing is that being lazy with your blowup yak will probably cause it to last a good deal less time than it should - that mould can deteriorate the fabric which it's made of, and if you use it in salt water the salt can abrade it and make it break down as well.
To do it properly, I suggest you have a couple of dry towels - two or three at least (big ones). With the boat still inflated, remove everything you can (seats, net bags, etc.) and dab it dry all over.
Depending on the model of your kayak the next steps may vary - with something like a Sevylor Colorado or AdvancedFrame with an inflatable floor, you should deflate the floor and tip it over to allow any free water to drain out from between the floor and the side bladders.
You can also take this opportunity to wipe away any debris that gathers in the gutters between the floor and sides. Remember, change to a dry towel when the one you're using gets wet.
The next thing is to fully deflate it, mop up any more excess water, and then leave the yak to dry before rolling it up and packing it away. Overnight should suffice - a good tip is to use a stepladder or something, especially if you're short of space: set up the ladder and drape the yak over it, upside down.
Now, if you're going to take the boat out again within a few days or a week, it isn't necessary to go through all of this. Just draining out any excess water should be fine. But if it's going to be a month or so, you do risk mould growth if you don't thoroughly dry it.
Although the above only takes a few minutes of work, if you're going to be using the yak regularly then I suggest that you just leave it out to dry: leave it inflated, until the top is dry, then turn it over so any more excess water can drain out, and leave it to dry upside down. If you're fussy, you can use a towel to mop up any more free water as you deflate it and pack it away.
You should definitely clean and dry your inflatable thoroughly if you intend to store it for any length of time but if only for a few days to a week, then this will be sufficient. I don't know if it will decrease the lifespan of your boat, but I suppose it might - especially if you're using it in salt water.
Use with caution!
If you're storing it for a longer period, do the following and then go through the steps I outlined above (the proper way), to get it nice and dry and ready to store.
So, first of all, give it a good washing - you'll probably have to do this at home, either with a garden hose or a bucket and sponge. Actually, a bucket and mildly soapy water is the best idea - you can probably get special kayak soap, I use dish soap. Just a little bit.
Then rinse it off, trying to get all of the soap and any grit or sand or leaves off. Get into the crevices, especially if you use it in salt water.
Then dry it (the proper way). After that, it's ready for storage.
If you're storing it for a longer period, you could put some dryer sheets in the bag with the yak - apparently, mice don't like the smell of drier sheets, and it will discourage them from nesting in or eating your boat.
Another thing you can do is put silica gel or homemade desiccant (use Epsom salts dried in an oven) to keep it dry, especially if you're storing it in a humid environment.
A lot of pumps have a deflation port in them, so make use of that when packing your kayak up - as you're folding, use the deflation valve to suck out as much air as you can to help you fold it smaller.
Finally, if you have succumbed to mould and have black stains on your yak, try using vinegar (spirit or white vinegar) to clean them off. Vinegar also kills off the mould, so you can use a solution of it to clean your entire yak.
I hope this has been helpful to you - happy storing! I mean, happy paddling!