As far as parties go, you can quite literally have success with any party composition - I've done 6 paladins, (MP party), 5 cleric/mages, 6 ranger parties and so on. They do require different tactics, though of course. Having said that, almost everyone finds it easier to have a thief who is good at dealing with traps. Having 1 arcane magic party member and divine magic party member is quite handy as well.
As far as getting the most of the game - I would do what you find the most fun, regardless if it's "best" or not. Some people love to explore - if that's you by all means do so. Some people love to role-play - if that's you, by all means do so.
In BG 1, ranged combat is king - absolutely everyone (except dual-wielders I suppose) should have range weapons ready to be used, when needed. They are extremely useful against powerful melee enemies like bears, as well as quite helpful against enemy mages, and ghouls/ghasts, who have the dangerous hold ability.
Definitely use your limited resources, like potions, scrolls, and wands, against strong enemies, typically enemy parties.
I'm not sure what your skill level is, but hopefully you find this useful.