Export the GEDCOM from Geni.com
Click on https://www.geni.com/gedcom/export
Select the Export Forest option, and follow instructions.
Wait for your GEDCOME file to be created (you will be notified by email).
Download the GEDCOM file.
Remove non-ASCII characters from GEDCOM file
If your GEDCOM file contains non-ASCII characters, you'll have to remove ...
The MyHeritage site has an FAQ entry for this. It walks you though the progress with pictures and everything.
Summary: You goto to File -> Export GEDCOM, fill in the dialog until you get to the "Pick content" section. There you can pick the option Include only selected people. Choose the person you want the tree to start with and click Edit to select ...