Usually, many of us would either grab the password from the back of our routers (which is a bad idea; don't have your password in the open where someone can get it easily), or dig up a piece of paper somewhere (a better option). Either way, there's an easier option: QR Codes!
As more and more companies shift to using QR codes, so do phones and computers come along that can read these codes with ease. In fact, you can generate one for free, and then print it out and frame it, and hang it on your wall. That way any relative of friend can just walk in, and scan the code and be online in mere seconds, instead of minutes.
There is a great tool out there, called Online QR Code Tools, that allows you to enter your routers SSID, encryption type, and the router's password. Once done you hit the generate button, and then outcomes your QR code. You can choose to get it in just about every major image format, even in vector form if you like.
And with that, all you have to do is hang this on the wall and let your friends and family scan it, and they'll be online in no time, without the help of you. I tried the tool myself, and it works great. So I definitely recommend this. Let me know in the comments below if you'll use this.