When I experience brain fog, I do best if I limit my environment - usually no music (maybe low volume only) or television on, lights adjusted, only talk with one person at a time if at all. I can't really multi task when foggy. I'm especially not good at talking on the phone.

Hopefully I'm able to make sure I've had enough to eat and drink. Slowing myself down helps so that I'm not trying to do too much with limited abilities. Pacing my activities can help, if especially foggy I might choose to put off anything complex and focus on something simpler.

Sleep can help, sometimes light exercise and fresh air helps too.