Tips for painting old plastered walls?

http://www.housepaintingtutorials.com/wall-painting-techniques.html

Embrace the imperfections and be grateful you live in such a fantastic home! My mom's house was built in the mid 20's, with lath & plaster. I used a good washable satin on the walls.

I lived in a house that is over 100 years old. As long as the plaster is solid, we just painted it as best we could. To me, it’s part of the character of the house!

You can skim coat the walls for a smoother look. Here's an article to help you out:

https://www.property24.com/articles/how-to-smooth-out-textured-walls-in-old-houses/22380

You could texture the whole wall first, but the imperfections are part of what give old houses their character.

Here is a cool technique to quickly skim coat a wall.... gonna use the roller on my next wallpaper removal job..... looks like it would save a ton of time. .... https://www.youtube.com/watch?v=jeGWbgAUvCM&t=715s

Here Jane explains working on skimming a plaster wall with the right product.... https://www.youtube.com/watch?v=Mob1K_P_L8U

We love our 113 year old plaster walls and ceilings! I don't notice imperfections but perhaps I consider them character and as Naomie says, embrace them!