Using the antiquated word "Well" (or it's lower counterpart "Welp,") is decidedly unfashionable and wholesomely old fashioned. The expired interjection has been demoted to oblivion, with the new "So" darling happily taking its place.
If someone asks you, "Can you please explain why the sun is yellow?" don't bother to buy your time with the dinosauric "Well;" instead, start your soliloquy with "So," so as to set up your listener for the awesomeness which you're about to dish out.
Ready to take your "So" use to the next level? Consider drawing out your "So" (but only ever so slightly) to create a subtle, yet dramatic effect which should keep your listener hanging on your every word, especially that one. It makes the passing-on of wisdom so much more snobbish but oh-so-satisfying.
So now you know. :)
