As the above person said, the most common combo is Fo/Te, which is your standard caster build. You need to get used to dodging though, as you'll be fairly squishy. Most of the other class combos don't have any damage bonuses that apply to techs, so they're inferior as they won't increase your damage. Hunter as an example has Fury stance, but that only applies to striking/ranged damage, so is useless for a Force.
Another option is Force/Summoner, but I don't know much about them. I think they are less squishy than Fo/Te, but might so less damage and/or are harder to play?
This is your standard Fo/Te build: https://bit.ly/36RCSf1
I've leftover points on the Fo tree that you can put into either the rod or talis skills based on your preference. For example, Talis Tech Bonus is a must if you use talis, as it's a flat 20% damage bonus. But as a rod user you can skip it.
You want to focus on skills that give a % boost to damage, and they're multiplicative. So on the Force tree the skills I've chosen will give you:
1.27 (elemental conversion) * 1.10 * 1.10 * 1.10 * 1.14 * 1.2 = 230% damage with ice/fire/lightning (you'll get the same for the other 3 elements from the Te tree). Plus Elemental Precision hit on the Te tree is an additional 1.2 = 277%. And if you use Talis that's an extra 1.2 = 330% damage.
On the Te tree you focus on wind/light/dark, and the PP regen skills. Without the PP skills from Te you'll probably have issues with PP regen.
*note: For elemental conversion I've used 1.27 as that's for a non-matching weapon with 60 element factor. If it were matching it'd be 1.3. If you only have 50 element it's 1.225 and 1.25 respectively.