Crossing logs, rocks and small obstacles is a natural part of enduro riding. There's plenty of those in the woods and crossing them safely and fast is the goal.
The primary objective is to drive the front wheel over the obstacle: the rear wheel will generally follow without any drama.
If we're looking at a very small obstacle, like a branch, you can generally ride right over it without any special technique. The only thing I would do is to move my weight back a little, so the impact of the front wheel is not that hard... You can always underestimate the impact and having less weight on the front will keep it on the safe side.
With larger obstacles, the biggest mistake is usually impacting it hard with the front wheel, resulting in either your being thrown over the handlebars, or at least the bike shaking violently and you possibly loosing control.
You need to at least ease the front wheel over the log or, the more advanced technique: lifting it over (wheelie).
To ease the front wheel over the obstacle, you must unload it, so move your weight well back on the bike, but not so back that you are on the edge of control. You can do this while slowing down just before the obstacle.
Next, hop the bike over!
You want to hop down on the bike and compress the suspension, just before the log, letting the rebound of the front suspension lighten the front wheel over the log. You don't need to lift the wheel off the ground for small obstacles, just lighten it.
The other way to hop the bike over is to quickly apply the front brakes just before the log - this will also compress the front suspension and you want the rebound to again lighten the front wheel over the log.
Maintaining momentum while crossing the log is very important - this video makes that aspect very obvious:
Both hopping techniques can be and should be practiced without logs and obstacles - it should be obvious by now that the timing is everything: if you hop any sooner or later, you will not achieve the proper lightening of the front wheel over the log or obstacle: you are looking for the rebound of the front forks to be at a maximum when over the log - so when practicing, focus on the timing of it.
Also, through practice you will figure out what sizes of logs require what technique. How large can you take at full speed, when and how much to slow down etc.
The next step, the other technique is to complement the rebound of the forks with the throttle and wheelie over the log - this works on bigger logs and rocks and will be the subject of the next post here.
Avoid getting kicked by the rear of the bike - the rear will come up when crossing the log and you just moved back (which will also lower your butt closer to the seat) so... this could happen:
Also - always try to get the log perpendicular - any time you hit the log at an angle, especially when wet, you run the risk of the wheel just sliding off it instead of hoping over
The last thing to avoid is to give too much throttle when the rear wheel is over the log - there's usually pretty poor traction there...