
I. "Boost": You line up stuff that boost the same stat to high levels.
For example: Elf Sorcerer of JJ can reach very high amounts of Max Mana. Dwarf Priest of JJ can get to high levels of Health. Goblin Fighter of TT can amass a lot of extra XP.
II. "Reinforce": You try to improve two related stats, that are multiplied for total effect.
For example: Orc Rogue of Taurog can boost both Damage and Attack%, reaching very high total damage. Gnome Sorderer of Mystera can boost mana to fairly high levels, and then refill it many times. Halfling Priest gets a hefty bonus to Health and to refill effectiveness; and gets a lot of refills.
III. "Enable": You try to push a stat to an acceptable level - working off a handicap, or just boosting it beyond average - to enable another stat to really shine.
For example: Dwarf Rogue eliminates the Rogue's drawback. A Berserker worshipping Mystera works similarly. A Dwarf Assassin who pushes Health just enough to be able to take a single hit from a high-level monster - and then uses poison regen-fighting to wear it down.
IV. "Compliment": You try to push two unrelated stats to allow you to shine in both challenges needing one - or the other - stat. While one stat does not directly impact your ability to take on challenges of the other stat, it may allow you to spend resources more optimally.
For example: a Gnome Priest with +Mana items/boons will have a balanced refill available, maybe getting 400% to both (boosted) bars. An Elf Assassin can focus her spellcasting on higher-level opponents, and save resources on lower-level kills.
V. "Indirect": Perks that have a synergy with the same third thing. Even though they are unrelated to each other, having both might be beneficial to a character who expects to be strong in the third thing they synergise with.
For example: Alchemist Scroll, Trisword and Alchemist Pact have different effects and are only related to each-other in the sense that quaffing a potion will trigger their effects. They have an indirect synergy that is exploited on a Halfling, for example.