There is one very efficient trick I will call reverse axe/hatchet. (No idea if this technique has a proper name, feel free to correct my answer.)

The problem with a hatchet is that it is quite light weight, so there is not a lot of force available for splitting logs. The trick here is to inverse this scenario, so that the weight of the log will work in your favor, i.e. do the splitting for you.

First place a goot hit with your hatchet/axe into the center of the log (it must get firmly stuck!):

  ===========   
  / \
------
|    |
|    |

Then flip the whole thing, so that the log is above the axe head:

|    |
|    |
------
  \ / 
  ===========   
   ^
   X

Now swing the whole thing upside down so that the back of your axe heads (marked X above) hits chopping block. (If you don't have a chopping block, use a sturdy flat log.)

This will make the entire weight of the log work in your favor, instead of only the comparably light axe head.

Things to watch out for:

• The block can fall of/fly away if it is not firmly stuck to the blade. So don't overdo your swings and keep clear of people.
• Never hit your axe head on a rock. Use a chopping block/log or similar.

There is one very efficient trick I will call reverse chopping. (No idea if this technique has a proper name, feel free to correct my answer.)

The problem with a hatchet is that it is quite light weight, so there is not a lot of force available for splitting logs. The trick here is to inverse this scenario, so that the weight of the log will work in your favor, i.e. do the splitting for you.

First place a goot hit with your hatchet/axe into the center of the log (it must get firmly stuck!):

  ===========   
  / \
------
|    |
|    |

Then flip the whole thing, so that the log is above the axe head:

|    |
|    |
------
  \ / 
  ===========   
   ^
   X

Now swing the whole thing upside down so that the back of your axe heads (marked X above) hits chopping block. (If you don't have a chopping block, use a sturdy flat log.)

This will make the entire weight of the log work in your favor, instead of only the comparably light axe head.

Things to watch out for:

• The block can fall of/fly away if it is not firmly stuck to the blade. So don't overdo your swings and keep clear of people.
• Never hit your axe head on a rock. Use a chopping block/log or similar.
• If your log is too big to fully split when your entire axe head is buried in the log this technique will not help you and you will have to get your axe 'unburied' from the log which can be a pain.