I would add to the excellent information from Guppy to also be wary of flying in conditions where you know you will hold ice to the ground or the MSA.
I can remember a trip in a light twin where I had encountered a lot of ice airways. I left the weather but still had a long way to go.
The speed had decayed so much that I asked the controllers whether I could descend below the airway for Ten minutes so that I could melt it all off the airframe.
I then climbed back up and setup a normal cruise.
Some ice will vapourise off once clear of ice and cruising but you can carry a substantial amount of airframe ice.
On another trip into Scotland I could hear large jets reporting ice in the holds and on approach. I was then given a descent to take up a hold. I delayed that descent for as long as possible to keep in clear air on top. Descending into the clouds into the hold it quickly became apparent that unlike the larger aircraft I could not hold for very long. Do make it clear to controllers if they ask you to do something which will cause problems.
Ice can be scary because it is inconsistant, can take you by surprise and can build very quickly. In larger aircraft which climb at 3000 fpm you can quickly climb through those ice layers. In light singles or twins you hang around in there with aircraft which are least equipt to deal with it.
Pace