I've hitchhiked for on week in Iceland. If you are on the ring road or in the main gravel roads (for example the F208 to Landmannalaugar), you shouldn't have to wait too much. There is one time where I waited for 2 hours, but other than that it was often 30 minutes max.

The bus system is pretty extensive and can bring you near where you want almost every time, but it can be a little expensive (in Iceland, all is expensive). I would consider a mix between bus (to get out from Reykjavik) and hitchhiking (quite easy, cheap, and you can meet tons of nice people).

The north-west (the fjords) can be pretty rough when hitchhiking given that there is'nt much cars passing by.

[![Road][1]][1]

*Sometimes it's nice to wait for a ride*


  [1]: https://i.sstatic.net/ARb63.jpg