axeil has issued a correction as of 23:11 on Feb 28, 2016

• ALWAYS boost Abolitionist support when and where possible. Even in the South; you won't win those states with that, but it boosts your consistency and conviction scores which helps elsewhere. Don't forget to use the "Christian neccessity" modifier for best effect.
  
  
• 1840 is probably the easier of the two scenarios to win. I've gotten to the point where I can pull it off fairly consistently barring RNG fuckery. You will need to win all the Free States to win the election, since it's virtually impossible to win any Slave State. If you don't get a majority of electors, you get the "Congress decides" ending and you lose.
  
• Van Buren is being attacked from all sides and is generally not a real threat on his own. Join in with attacks on his economic record and his elitism (but avoid anti-Dutch sentiment, since that would impact your own consistency score).
  
• The key to winning the Free States is dealing with the political machines there. You can try to get them on your side or fight them, both work, but working out which is better depends on the state and apparently the RNG as well. The exception is New York: you have to fight the Democratic machine here to even have a shot at winning the state instead of the native van Buren. Not just once, but several times. Every victory reduces its influence, so keep it up until you can win NY.
  
• Harrison is a lot tougher to take down since he spends a lot of time being elusive and unable to be hit. However, there are a few openings and you should focus on those. 1) If you kept your consistency and conviction scores up, you can somewhat effectively hammer him with attacks targeting his consistency and conviction scores. 2) If he uses his attacks against Freemasonry, he uses the "Christian morality" for those which means you can counter with a "Hypocrisy" attack which damage scaling to your own consistency stat. 3) Also debuff his support in the Free States. Focus on where it would prevent you from winning a plurality; remember that demobilizing debuffs work better than charms with his supporters.
  
  
• 1844 is much, much harder; I've not yet been able to pull it off. Clay is easy to elimate as a threat, but Polk is incredibly hard to take down.
  
• Import your save! You need every boost you can as you won't stand a chance otherwise. When choosing your incumbent bonuses, take every boost to Abolitionism available, anything that debuffs the Democrats, and anything that buffs your own party - in that order of preference.
  
• Again, you want to win all the Free States while ignoring the Slave States, unless the RNG distributes your Abolitionism boosts in a way that gives you a shot there.
  
• Clay can effectively be knocked out of the race by attacking the Whig party itself. It's actually quite easy to break it up since the Polk's AI will do the same. Figure out which parts of the Whig coalition can be charmed into supporting you and do that to get a much needed boost.
  
• Polk is a nightmare. He's super aggressive and even if you imported your save and start as incumbent, he will dictate the pace of the campaign and you will be mostly reacting. With an imported save you should be strong enough to minimize the impact of his "Extend the Missouri compromise" attacks. In fact, you should be strong enough that you can counter his "Indian removal" attacks to good effect.
  
• The real threat, however, are his various Expansionism type attacks and I've not yet found the right way to deal with them. If you react to "Fifty-Four Forty or Fight" with support, he will gain more support than you do, but opposing it or - worse - ignoring it is effectively a terrible debuff; I think you're better off supporting here. "Annexation of Mexico" is easier to deal with and can actually backfire on him. If there was a way to manipulate his AI into doing it I haven't found it yet. As is, you have to hope you get lucky with the RNG.
  
• You likely won't get many chances to act rather than react. If you do, I've found attacking him on issues other than the above is rather effective, although I've not yet figured out which attacks are the best here. If seen a post somewhere (sorry, I don't remember where exactly; probably another board) that suggested applying the "Anti-Jacksonian" damage type to these attacks. It sounds like it could work, but I haven't tested it myself yet.

Hodgepodge has issued a correction as of 08:10 on Mar 1, 2016

Nix Panicus has issued a correction as of 02:57 on Mar 2, 2016