Shooting in RAW is always a good plan, but if you don't want to use the storage space, or don't have the software to deal with it, it's not the end of the world. Not sure why your images are coming out this way, Nikon is generally very good at AWB, especially in out-of-doors situations. To start, try matching your WB setting to the conditions (sun, cloud, shade, incandescent, etc).
You also need to be able to "see" what the final colours should look like, and then you can correct to them. 99% of the time using the colour-balance tool (or equivalent on your software) will get you decently close; simply adding/decreasing the blue/yellow levels will suffice. There is also lots of freeware (Gimp, Raw Therapee) which may make this easier. Again, remember that this is something that's fixable in post, it's not like you've cut half of of someone's arm off.