I've seen so many posts here about what is a good tune, who does it, et cetera, that I've decided to put together a little do-it-yourself (who else do you trust to screw things up?) guide to selecting the best airgun tuner for you. This was put together based upon years of unrelated experiences.
First, you want to select a good tuner. How to find one? Search the dealers' websites for reputable airgun bloggers.
Now you can go shopping.
Do you want to go with a big name, like Cheif AJ?
I prefer the small volume tuner as they seem to take greater care in their custom work.
Whoever you chose, be sure to get a few references. Here's one from the shop, above.
That sold me! But, if you can, it pays to take a look at their website. His premises can say a lot about him.
As well as his workbench. (Remember, that is where the magic takes place!)
So, you've chosen a well-known tuner. (Don't let sour grapes posts deterr you.)
Now it's time to send your baby off for major surgery. Be sure to pack it well!
Let's see what he can do to improve your mule-kicking, teeth rattling, poor excuse for an airgun.
He'll start by examining the bore. After all, that's the most important part of any gun.
Oh, well. These things happen. After you've taken him to the hospital, get a referral to another trusted 'smith.
He'll probably suggest you upgrade your spring and give you an assortment of power levels.
But most owners will want that new ultra-magnum JM spring to wring out every FPS possible. Here's the latest as shown by the master, hisself.
Next, he'll check for factory imperfections like the dreaded barrel droop. Look at the droop in this stock Diana.
Now see how it's been PROPERLY adjusted by the master technician. See how he's got it pointing up in the proper direction?
Once he's installed all the new innards and bent the barrel, it's time to accurize. He'll start by examining the test target you shipped with your gun. (You did, didn't you?)
Next come extensive testing using a variety of pellets.
Finally, he'll find just the right balance of power and accuracy.
Voila! Here's a happy gun owner with his newly improved airgun, ready to test her out.
The first thing you want to do is some serious shooting. Be sure to evaluate your targets carefully.
Now you are ready to take on some game in the field! Start modestly.

(No Crosman employees were injured in the making of this thread.)
Then you can work your way up. What better use for all the EXTRA FPS?
Heck, go for it!
Even try some always popular penetration tests.
That's some punch you've got there!
Now you're a real airgunner! Get out there and show off your pride and joy!
(But don't feel bad. Within a couple of days you'll meet someone who's gun has even more FPS than your's. Here's one that operates at the speed of light.)