My guess would be SP's are going to be more focused in the present and less on abstractions, where as NJs will be more focused on the future and the big picture. But thats not to say NJs can't be present or SPs cant think long term, but rather the culmination of their behavior over time, what do those patterns reveal?
The SP's and NJ's I know both can have a goofy sense of humor, but SP's generally appear more laid back than NJ's. NJ's can appear very deliberate, and somewhat more serious (even INJ's who are dominant introverted perceivers, they get stressed more easily; at least the ones I know.)
SP's I know - typically say things like "why worry about the future, enjoy the present moment, live life for today."
NJ's I know - typically they know what they want to do, and even though they might not talk about it, they have it planned out far into the future. (this is with everything, including relationships) NJ's also often talk about "humanity as a whole" or make an already generalized topic even more generalized.
-SP's, especially ISP's (IP's in general, are going to want to delve more into specifics and details.)
*Feel free to correct me if I'm wrong or have stereotyped