Depending on the actual material you want to glue there are many options. If it's paper or cardboard, Mod Podge or white glue that you used in elementary school will work fine.
But what if it's a combination of different materials, such as plastic and metal? There must be a specific glue for that, surely?
Choose the right glue, with the properties that will enhance, not detract from the finished project.
I've tried pretty much everything, and there are many more things that I don't know. Something I've learned; Don't use Mod Podge for everything. Test it out first, to see if it's going to work.
Best used on paper or cardboard, Mod Podge comes in several different finishes; semi gloss, matte, etc., just like paint. You may find you prefer one over the other types, or use them for different projects.
My main complaint about most kinds of glue isn't the glue itself. It's the package!
Gorilla Glue is a great glue, but it's almost impossible to squeeze the bottle. I usually let it drip out onto something else, then spread it with a toothpick or piece of wire. It is almost impossible to get it off your fingers. It just has to wear off.
Another thing to keep in mind with Gorilla Glue is that it expands as it dries.
Don't leave it alone for a minute!
Wipe off the excess a few times until it stops expanding. This can be a good thing, as it fills in any cracks or spaces, but it can also spread pieces apart.
Clamps are our friends.
Another candidate that's tricky to use is two part epoxy. This product usually comes in two tubes, bottles or a syringe with two parts to it.
It only sticks once it's mixed, that's why I get the five minute kind, which gives you enough time to actually mix it, spread it and get the parts of your craft in the right place before it dries rock hard.
My latest project is to try Kinsugi, or gluing a broken dish back together using a method of glue with gold to make a distinctive mend on a fragile piece of pottery. Don't hide the damage, enhance it!