As an individual voter, there is very little you can do to keep your own vote secure and safe from hacking, manipulation, or fraud. The most effective action you can take, if this subject is important to you, is to contact the elected officials in your area who are actually responsible for securing elections against hackers and raise your concerns.
On a personal level, here are some tips to secure your vote and make sure it counts:
If you vote via paper ballot and optical scanner:
Read the instructions on your ballot, and make sure that you mark the ballot in the required fashion.
If given the option, scan the ballot yourself. Do not leave the ballot scanner until you see that your ballot was accepted.
If not given the option to scan your ballot, ensure that your ballot is placed into a tamper-proof container by poll workers.
If you vote via a DRE voting machine:
Familiarize yourself with the touchscreen, push-button, or dial controls.
As you vote, pay close attention to each screen, and make sure the machine is correctly registering your choices.
If provided with a confirmation screen, carefully go through the list to make sure that it lines up with the choices you made.
Ask poll workers if the machines are equipped with a voter-verifiable paper trail. If they are, make sure to examine your ballot receipt carefully when you are done voting. If it doesn't match the actual choices you made, you may be able to mark it spoiled and try again. If it still doesn't match, bring it to the attention of poll workers. The machine may be calibrated improperly.
If you vote via mail:
Voting via the mail is generally considered to be secure, as the primary vector for attack involves stealing and altering ballots after they have been placed in a mailbox or drop box.
If possible, avoid putting your ballot in an unsecured personal mailbox.
Use a secure mailbox if possible, or take your ballot to a designated drop off point.