If you know a band, artist, filmmaker, author, restaurant owner, actor, or some other enterprising person and want to support them in their undertakings, stay off the guest list. Pay to see the show or movie, buy the book, or pay for your meal and tip well, just like everybody else. This means a little to you and a lot to them.
Here's a fairly realistic example:
Say you know a band that has a gig at a small club. They put up fliers, send out an email, and maybe the club puts them on the schedule in a print ad in the local paper. You think the band rocks and they're your friends anyway, so you, being ever-helpful, tell a bunch of people, of whom 2 turn up for the show.
20 people turn up either because they were already there or they came for the show. There are 10 people on the guest list. You turn up with your boyfriend and 2 friends. You go in first, find the drummer, and ask if they can hook up the people you've brought and just let them in, which the drummer does. Most of others on the guest list do the same thing. A few come alone, most with one friend or significant other, but one brings a whole crew of people from the next town over, which yields an average of 2.5 non-payers for every person on the guest list.
Now we have 45 people there—a nice number for both the band and the club if they had all paid to get in—but more than half of them got in for free. This could easily be the difference in the band being able to book another show at that club in the future and whether the band barely covers gas money to and from the show or has a nice little chunk to put into making t-shirts, studio time for their next CD, or a touring fund.
You go up to the band's merch table after the show to tell them how much ass they kick when the singer says, "Hey, thanks for getting the word out and bringing people! Here, have a free t-shirt."...
If you really want to support your friends' artistic or small business endeavors, it's important to put your money where your mouth it.