As someone previously mentioned,
"Turn Left at Orion" would be a good resource, because everything in TLaO is viewable through a 4" telescope. Further, there are pencil drawings of what one should see through the scope, which is a much more accurate depiction than what a person sees in magazines such as "Sky and Telescope" and "Astronomy".
I would certainly plan ahead. There are really four categories of targets easily accesible with a 4" scope: (a) moon, (b) planets (really, just Saturn and Jupiter) (c) *some* deep sky objects and (d) the sun. Looking for binary stars, comets, variable stars, and such is just not going to be very fruitful, except in the very best of conditions with a very good instrument. Using general resources on the Web or the Sky and Telescope web site specifically (or the magazine for that matter) can tell you what is even available for your planned evenings and times. It's been awhile since I looked at TLaO, but I think it's broken down by late evening viewing for each season. In other words, what the Eastern sky looks like at 11:00p in winter is very different from what it looks like in summer.
Weather can be your best friend or worst enemy, for obvious reasons. But picking a night of full moon to look at deep sky objects is equally bad. This is why planning ahead of time is so important. You can also set expectations ahead of time of what will be observable, and what it might look like through the lens. Again, the beautiful pictures from Hubble are a far cry from what someone sees in a telescope. So, it can be very easy for a new observer to feel let down if their expectations aren't addressed early.
If you go for some deep sky objects (See the Messier Catalog), make sure you spend a night before hand figuring out how to find these objects on your own and what they look like. You don't want to be fumbling at the telescope trying to the find Orion Nebula while everyone just stares at you, and then not know if you have even found what you're looking for. Same could be true of Saturn and Jupiter, but it's much easier to tell if you've found the right target. The moons of Jupiter, albeit tiny points of light, are always interesting, especially if you observe on consecutive nights. The moon goes without saying. Moon observation is a hobby unto itself.
Observing the sun is really dependent on sun spot activity. If there are sunspots to observe, that's at least something to see. Otherwise, through a plain 4" scope, the sun isn't particularly interesting aside from a bright orb that looks like a balloon (look up Coronado telescopes if you really want to see how amazing the sun can look through a telescope. The pictures you see is what it looks like at the lens).
good luck. hth,