What processes do I need to carry out before repainting my wall?
Two long for a comment so added as a second answer: a photo of the walls in question would be helpful, I am used to working in 1900's and newer homes with these type the walls have a 1/2" to 3/4" of plaster or sheetrock the only way to make them sound less hollow is to have them filled with insulation. If you want to get a solid brick or stone wall sound an overlay sheeting may help like a faux brick wall , the only problem with these is I could always see the seams. To get rid of the bumps it depends on what type of wall it is but both start with sanding as I outlined sheetrock would use a finer grade of sand paper compared to plaster. Joint compound can be used in both cases for a base coat to get things close but a super flat finish would require topping compound much finer and easier sanding.