How to shoulder a bike?
I ride a lot of trails where it is almost impossible to ride up and sometimes not even practical to push the bike up, and it is easier to carry. I've got a full suspension mountain bike with no space inside of the triangle, so it is not possible to shoulder it. And carry a bike on my back, rather than on a shoulder. Bottom tube is resting on my shoulders with rear wheel on right from my head and front wheel on left from my head. 

Like that:



It helps if you have a backpack, as the bottom tube rests on it. After some practice you can have both of your hands free, while bike comfortably sits on pack. This way bike does not get in your way and you can hike quite a big distances.

UPD: This position is not the quickest to put the bike up, but I find it the most comfortable when climbing. To get the bike up, stand on non-chain side of a bike, place left pedal (closes to you) in the lowest position, grab with one hand the left crank and fork stantion with the other hand. Lift the bike over your head and on your shoulder/backpack.