Personally, I think the best thing that could have improved VOY was for the series to come much later, probably just as DS9 was wrapping up, and to be in first-run syndication rather than on UPN.
But things that I would have done differently:
1. The ship wouldn't be in the Delta Quadrant but in a very distant part of the Alpha Quadrant so far from Federation space that you really get the same effect of it being the only ship out there. The crew wouldn't be trying to get home, but they would get homesick now and then. There would be Klingon and Romulan ships in the region too, but only one of each with reoccuring characters.
2. The XO would have been a woman, and yes, I would have cast a young voluptuous type in the role as simply a physical counterpart to Janeway in the same way Riker was so taller and younger than Picard.
3. No Maquis. It would have been an all-Starfleet crew from the very beginning. There would be occasional conflicts between characters though.
4. No Borg. I know UPN loves 'em, but the idea that a single Intrepid-class ship can do what 40 starships couldn't just strikes me as funny...
5. No forgettable aliens of the week. There would only be about four or five alien races in the region of space the Voyager
would encounter on a regular basis. Any other alien races would be Human, Vulcan, Andorian, etc. Let the major conflict be about a new hostile alien race coming in to take over the entire region and the Voyager
organizing a reluctant interplanetary coalition to stop them.
6. No Neelix. No Kes. No Seven-of-Nine (the aforementioned female XO would serve as the show's reguired sex object).