Depends if they want to go on the defence of offence (in no order).
GOP (Offencive strategy): Minneapolis MN, Las Vegas NV, Virginia Beach VA, New York City NY (this last one is very bold, but could help in the NE)
GOP (Defencive strategy): Pittsburg PA, Atlanta GA, Houson TX, Phoenix AZ, Macomb County MI, Jacksonville FL
DNC (Offencive Strategy): Atlanta GA, Charlotee NC, Philadephia PA, Cleveland OH, Dallas TX, Miama FL, Phoenix AZ (this one seems a bit too bold, and I think Arizona would be a better target in 2024).
DNC (Defencive Strategy): Alexandria VA, Minneapolis MN, Denver CO, Seattle WA, Los Angeles CA
If things look bad for Trump in 2020, he should probably go to either Michigan or Pennsylvania. If things look good, Minnesota and Nevada look like ripe targets. DNC should probably go on the offence unless things are very bleak. Atlanta would be a good one, especially with the state trending more democratic each and every cycle.
If GA and NC are targets, AZ certainly is.