I bought a flat recently which needed some modernisation. I started by taking the wallpaper off and scrubbing the walls with a view to painting them, but I'm slightly stumped as to what I need to do next.
The bottom section of the walls are plastered and have been painted over; the top sections are unpainted plasterboard. The walls are level and smooth to the touch with the exception of the white areas in the picture where the top section and bottom section meet (which I'm going to sand down) but both sections have a lot of very fine cracks in them.
Basically, once I've sanded down the white areas between the sections to ensure everything is level, is there anything else I need to do to the walls before painting them? I'm assuming I'll need to use a primer/sealer/skim with plaster, but am a total beginner at this sort of thing so don't really have a clue!