The easiest way:

$ mkdir build
$ cd build
$ cmake ../
$ make
$ make install

If the build fails because you're missing a dependency:

$ (Install any missing dependencies.)
$ make clean-all
$ cmake ../
$ make
$ make install


#### Bundled libraries
Ettercap now bundles the following libraries with the source distribution:
  libnet 1.1.6
  curl 7.29.0

We will build bundled libraries that Ettercap depends upon, so you 
don't have to! 

By default, the build system will search for system-provided libraries. If it 
doesn't find the particular library it wants, it will build the library, itself.

# To disable the use of bundled libraries:
  $ cmake -DBUNDLED_LIBS=Off ../

# To disable the searching for system-provided libraries, and use 
# bundled libraries exclusively:
  $ cmake -DSYSTEM_LIBS=Off ../