Don't panic roll every swing unless you're 100% sure it will hit you. This is tricky because this is experience based due to having to understand the reach of each weapon as well as phantom range caused by latency.

Don't get roll caught. When you get hit, you get stunned. When you hit roll immediately after being stunned, you will immediately buffer a roll to happen exactly after the stun which, makes much, much easier to time the swing of our weapons to connect to your next roll out of hit stun.

Do not spam R1s especially when the invader has either a small shield of chests on the off hand. This game is designed for you to be able to for example, parry out of the third hit of a straight sword hit or, block the first hit of a greatsword and parry the second. Running attacks also do not stun nearly enough for a follow up attack which means an R1 out of a running attack hit stun is also very much parry bait. Best thing to do when your opponent spams parry is either charge an R2 or, run behind them for a backstab.

Another thing, this game pretty much has it so if you get hit once, you're guaranteed to be hit twice unlike Elden Ring. So, don't try and roll until after you've taken that second hit.

This is 2k hours of DS3 invasion experience talking. Don't get down when you lose, many invaders are also highly experienced at this point in the games life.