Effective chemical is first step. We always start with neat Xtreme clean, then go on to solvents. It's surprising how many sealers Xtreme clean moves. Any solvents around edges and you are going to spoil paint.
As to tools, first for us is Cyclo twin head vehicle polisher, which can drive brushes or pads, with an orbital action, after that it's hand brushes & scouring pads.
Some mid-range honing powder always helps. At least it's slate - not too touchy.