Your goal is to increase the will save.
My recommendation is to make the race Elf or Half-Elf or Dwarf. Elves and Half-Elves recieve +2 bonus on enchantment spells which covers most of the Mind-affecting spells. Dwarves have +2 bonus against all spells and a racial +2 wisdom to increase their will save.
As a class, I would go with Druid or Cleric if you can because those classes have a good will save progress and their main Stat is Wisdom which will net a very good Will save bonus.
Top those with Iron Will and Improved Iron Will feats and that character will be very strong against mind affecting spells unless the caster is ridicoulusly high level or your rolls are very unlucky.
As a result, assuming you have a level 2 half-elf Cleric, with 16 Wisdom you have +10 Will(+3 Cleric,+2 Half-Elf,+2 Iron Will,+3 Wisdom) save versus Enchantment spells with a chance to reroll one once per day without any magical aid.
There are a lot more ways to incrase your mental resolve against mind affecting spells. Traits, items or playing a Paladin like Rob mentioned in his answer but It's difficult to deduce what is allowed in your campaign or what kind of character is suitable. I intentionally left out domains and Paladins because they are restricted to alignment or the Deity. This is quite a general approach that is suitable to any character.