Ive kept several outdoors over the yearsboat and motor having different reqiuirements.
Covering with a cover is good however after so many hard rains snows and freezing will draw the tarp down and hold ice,placing a pole from seat to seat or even a complete pvc frame inserted into seat pole holes will help keep it taught,make sure livewells dont have water in them as welll,if possible trickle charge the bateries.
Marine stable in the gas ,to keep it from turning,fogging if left unrun for quite a time.
A second tarp above the first and not on the boat from any object to another to help keep some rain snow off is even more help,keep plug out and if water or ice does get in get it out asap.
Sure some more tips will come in,it depends somewhat upon where one lives,that was good for ohio,or even tn,here in tn I can run mine a few times a winter so dont fog.