The GURPS 101: Patching Holes series is meant to help players avoid specific weaknesses on their characters. It also is intended to help players identify a series of increasingly broad and effective solutions to a specific vulnerability or issue.
Today, three scourges of player characters: poison, disease, and influence rolls.
Getting poisoned can be dangerous - the cyclical damage might be low, but it just keeps coming. Many of them come with penalties to resist, often very steep penalties.
Narrow Solution Resistance to Poison (+3)  or (+8) . For the fraction of a +1 to HT, you can get a much better HT roll versus poisons. Be warned: some poisons have no resistance check. Without Immunity to Poison, you're just suffering from the negative effects from those, no roll.
Wider Solution: Higher HT. At 10/level, it's a +1 to resistance checks against poisons that come with resistance (many of them). This more broadly impacts your character in any case. Combine with the narrow solution if immunity is out of the question but you need to beef up your resistance.
Complete Solution: Immunity to Poison  or Immunity to Metabolic Hazards  are the way to go. These are generally available for robots, androids, silicon lifeforms, and so on, but it's not always available for "normal" folks.
Like poison, disease can be a grinding death.
Narrow Solution: Resistant to Disease (+3)  or +8 . Like poisons, some diseases won't come with a resistance roll, and some might come with race-specific penalties as well.
Wider Solution: Higher HT.
Complete Solution: Immunity to Disease  or Immunity to Metabolic Hazards , if they are available.
One upside of being a PC is that social skills inflict penalties, they don't inflict reactions. Still, it can be annoying to have to suck up a -5 because someone Fast-Talked you and you want to ignore it and search him anyway, or Intimidated you but you don't want to give in to the fear.
Narrow Solution: Increase Will, at 5/level. This will help against and Skill vs. Will contest centered on social skills.
Technically, Fearlessness [2/level] is the narrowest solution, but it only helps against Intimidation. It's mighty effective against that, however, as it subtracts from the roll against you and adds to your Will to resist, make it twice as effective.
Wider Solution: Indomitable  is the next tier up. Unless someone has the appropriate Empathy ability (Empathy, Animal Empathy, Plant Empathy, or Spirit Empathy), influence rolls automatically fail.
Complete Solution: There isn't really one. Combine high Will with Indomitable, but know it's still possible for you to be influenced!