If they are in two pieces (hard shell and soft liner) then treat them separately, washing and drying the liner before putting it away in an airing cupboard or similar warm dry place.
You want to clean the shell with clean water and a little soap, to get rid of grit, salt and other deposits, taking extra care to remove all dirt from clips and moving parts.Rinse and dry thoroughly.
I store mine in my garage, on a shelf, in a boot bag to prevent insects or spiders making their home in them. The garage isn't heated, but this isn't generally an issue.
Update as per Nisan's comment:
Also go over the parts to make sure they are all there, functioning as designed, and properly tightened where they should be... It will save you the trouble of finding this out on the first trip next season
And (and this may sound silly) always store them in the same place each time - it may sound OCD, but I have specific places for winter sports kit, summer sports kit, etc - so I don't need to worry about hunting round for them each season.