Democrats Abroad Voter Information Team
This is a great site for U.S. citizens living abroad who want to vote absentee. https://www.overseasvotefoundation.org/vote/home.htm
Contact your county election official to find out requirements for sending absentee ballot requests and methods they use to send and receive ballots. https://www.overseasvotefoundation.org/vote/election-official-directory
Each election year, send an absentee ballot request, which serves all elections in that calendar year. You can also use the form to register to vote.
The method for delivering an absentee ballot request depends on the state and county. Some accept signed requests as an email attachment. All accept the federal application form. Some states also provide online forms.
You can vote at the local, state, and federal levels if you specify that you intend to return to the U.S. You can only vote at the federal level if you specify that your return is uncertain.
Whether you must declare a party in order to vote in a primary election depends upon the state.
Many counties make ballots available electronically (about 30-40 days prior to election day). Ballots must be printed and signed. Some counties accept faxed ballots. I try to send ballots with someone returning to the U.S. to mail (from wherever). Otherwise, I email it to a friend in the U.S. to print and mail. Depending on the state, postage is sometimes prepaid if you use the form and it is mailed from the U.S.
It takes more effort to vote from here but is doable.
I think voting is extremely important. Always.
Feel free to contact me at firstname.lastname@example.org if you need assistance. I will help if I can. I have a printer/scanner and a friend in the U.S. who is willing to print and mail democratic ballots.