I'm traveling to the US mainland for the first time in my life in a few weeks.
I am not overly stressed about privacy, but I have read that US immigration can really overstep their boundaries. Are there any simple specific steps to take on my devices to protect my privace when going through US border control?
Remove my main accounts from my phone/tablet and use dummy accounts? Or just removing my biometrics?
I think you're overthinking it. I used to go into the US often for business and I have never had any of my electronic devices searched. The best advice is to leave your phone at home and buy a cheaper pre-paid travel phone. Not because of privacy but what if it's lost, stolen, or confiscated? It's no big deal losing a burner phone.