1. "Permanent" is relative.
If you've ever tried to maintain a different hair color before, you know you have to keep dying your hair regularly. Hair grows, colors fade, and even permanent dyes need to be redone every month or so. There is no way to change your hair color without maintaining it regularly.
2. All dyes are not equal.
All dyes are not created equal, and not all colors of a certain brand are equally effective. Pirate? uses violet Pravana dye and it lasts months and months in her hair. I tried their "wild orchid" color and it washed out in a week. I use "fuschia shock" by Manic Panic and it lasts for weeks, but their "cotton candy pink" shade washes out much faster. I have found that the Manic Panic colors that look black or nearly black in their jars (in real life, not on the website) are the ones that have the most pigment and last the longest. It helps to try several different products to see what works best on your hair.
3. Say no to burny chemicals.
Permanent hair dye has a dark side, it's full of chemicals that burn your scalp. Leaving this type of dye on for too long can totally destroy your hair. Likewise, bleach or lightening agents can also dry out your hair and leave it horribly frizzy and gross. Unless your hair is really dark, you can completely forgo "lightening" it and just put your colors on over it. Pick a nice dark shade of your favorite color, you'll most likely end up with a nice vibrant tint over your natural hair color. Semi-permanent dyes like Manic Panic and Pravana's Vivids are non-toxic vegetable dyes that won't fry your hair and can be left on long enough to color almost any hair (or pet).
4. Longer is better.
The cool thing about using vegetable dyes is that they don't fry your hair, so you can just go ahead and leave them on indefinitely. I leave mine on for at least four hours, and often more than eight hours. The dye has to stay wet in order to keep working, so it helps to wrap your head in plastic wrap. Beauty supply shops also sell some nifty cotton ropes that you can stick around your hairline to help keep the dye off your skin.
5. Heat helps.
Heat is recommended by a lot of dye manufacturers to help set the color in your hair or make it brighter. I usually blow dry my hair for 10-15 minutes or until I get bored. Rinse well in cool water, and your color should last for several weeks.