The Washington Post has a front-page story up today on how to make sure your mail-in ballot is processed and counted: How to prevent your mail ballot from being rejected. This is advice that everyone needs to pay attention to — and make sure it gets spread to people who haven't voted by mail before, because the process is more complicated than voting in person.
If you need to request your ballot, do it early.
Read the instructions, and seek clarification from election officials if you are confused.
If you must sign your name, learn about signature matching.
Avoid stray marks, tears and other accidental flubs that could disqualify your ballot.
Return your ballot as soon as possible. If you do not want to use the mail, there might be other options.
Seek reliable information about the process from election officials.
Those are the basics; the article has the details. But I can sum it all up like this:
DO IT EARLY.
FOLLOW THE INSTRUCTIONS.
IF YOU HAVE ANY QUESTIONS, ASK.
Every state has different rules (and some have changed recently), and sometimes they vary by local authority. Election officials are non-partisan and dedicated to running a free and fair election with as many people voting as legally possible (I’m talking the local officials here, not necessarily the SoS and governors).
The people who run elections in your state, county or city are the best source of information about the voting process where you live. If you are confused at any point, seek answers on their websites, follow their official social media accounts or get in touch with them directly. Answering voters’ questions is part of their job, and they are responsible for making sure their communities have accurate information.
One point the article didn’t mention:
Track your ballot.
Many states have online resources that let you check up on whether your ballot was properly processed and counted. That’s yet another reason to vote as early as you can; not only do you defeat Trump's screw-up of the Post Office, you may, depending on the jurisdiction, be able to fix a mistake in voting.
Pass it around.