One more thing I might mention for first house Neptunians, is to look at the planet ruling your rising sign. It might be the same as your Neptune sign, or it might be different.
I don't know how many of you work with house cusp rulers but it really made a big difference to my ability to read charts. So, for example, if you have Neptune in Sagittarius and Sagittarius rising, what is happening to Jupiter by its house and aspects? If you have Neptune in Scopio in the first but Libra rising, then take a look at Venus by house and aspects. If these are stressed, you might see Neptune's less wonderful attributes; but if well aspected, you might be able to bring Neptune's inspirational quality to the arts or spirituality.
Then also, look at any aspects that Neptune makes to other planets. (Recalling that Neptune sextile Pluto is a generational aspect.)
I have Neptune square Jupiter and sesqui-square Mars, which seems to be a typical "bite off more than I can chew" aspect. I am generally happy to please people (Neptune in the first), but sometimes this means I believe I can do more (Jupiter's optimism, Mars's energy) than I actually can (or wish to) deliver (tension of the square). For example, this past year, I took on a leadership role in a local non-profit society. I worked hard at it (square) and actually we accomplished a fair bit, but I was thrilled to hand over the reins to someone else at the end of the year, because I just felt like I was knocking myself out (square) to do the work.
The planetary ruler of my rising sign (Mercury) has one positive and one stressful aspect in the 5th house, and I do think I have a vivid, creative imagination (Neptune<>Mercury.)
I have neptune in cap in the first, sag rising; jupiter in cap in house 1
sun opp saturn
venus opp saturn
mars conj saturn
jupiter sextile saturn
- definitely see neptune's less wonderful attributes

then I have:
moon sq. neptune
mercury trine neptune
venus trine neptune
neptune sextile pluto
- these seem better. I've read at one point at least what each aspect means individually, but I'm not sure how to guage whether or not the good outweighs the bad overall...