I'm all for looking at each factor in isolation. Why not? We know we'll have to synthesize it all eventually...but by pulling it apart we see all the pieces.
Jup in 1st takes up a lot of space, person is either loud, imposing, or charismatic. He is easily noticed. Often moralising and bringer of new ideas...
And I agree with Kimbermoon : "can generate judgement, intolerance, prejudice and rejection directed back at you by others."
If you do this you're going to end up with a whole bunch of separate factors that you're going to struggle to put together when the time comes. Trust me on that one. You've got to look at each and every piece of that placement (aspect, signs, dignities, houses, and yes, even duads) before you can even
attempt to interpret it in toto.
To show you what I mean, let's say that you go ahead and say that Jupiter in the 1st is loud, charismatic and is easily noticed. Ok.
But what if Jupiter is in Pisces trine Venus with Jupiter ruling the 9th? Sounds to me like this person is more spiritual and gentle than charismatic or loud.
What if Jupiter is in Virgo ruled by Mercury in Capricorn with Saturn squaring Jupiter? That would be less loud and charismatic and more meek, reserved, and "earthy".
What if Jupiter is in Capricorn square Mars who is in Libra? Sounds a little more dogmatic and domineering eh?
These are relatively general examples, but you get what I mean here. Even relatively small things like sign placement, house rulerships and aspects can change what a planet in a house means. You can't just say Planet A in this house means this thing. You're going to end up with a bunch of confusing contradictions if you do it that way.
Like I said, look at the sign, the aspects, the house rulerships piece by piece rather than making a general interpretation. Trust me, if you use general interpretations, you WILL end up confusing yourself.