Warm air rises and so naturally the walls and the roof are the first areas to consider.
Shed floor insulation.
Insulating the walls would be simple because they were exposed to the inside and insulation batting could easily be squished between the studs.
Measure the distance between the floor joists.
Insulating a shed will reduce damage to your stored tools equipment or boxes.
If you are installing insulation on a pre built shed you cannot simply drill a hole in the floor and pump it full of spray foam.
One of the drawbacks for spray foam is that you need backing for it to adhere to the surface.
However having a layer of insulation beneath the floor boards will contribute towards keeping the contents of the shed toasty.
This will be according to your shed plans.
Budget ability and experience also.
Is an effective but more expensive solution for floor insulation in your shed.
It can also make it more versatile allowing you to store plants or use it as a rec room.
I have a friend who lifted his unfinished shed to permit the floor to be insulated then lowered it back down.
Insulating the shed floor will help create a thermal barrier between the inside and outside air spaces.
Access to the underside of the floor though affects the options available for insulating it.
There is a nice video below detailing how to do this easily.
How to insulate a shed.
The best way to insulate a shed floor is in the building phase of the shed.
Insulating a shed floor is not one of the first things that comes to mind when insulating a small building.