Do you mean Auto-focus, or are you manually focusing?
Suggestions: Tripod. Wireless remote control. Self timer. Mirror Lock Up. Rear AF button and shutter button activated focus off.
Be prepared to spend a couple of hours on this. It will be worth it.
To refine the focus, depends on the camera, for the K1, you can adjust focus front and back across a range of +/- 10 from the defaults.
You'll need a test target. Put it at 25x to 50x the focal length of the lens (eg if you use that lens at 450 most of the time, your target need to be at about 35' to 75' away).
A few options that I've tried that can work:
A bunch of AA batteries with the lettering facing the camera, or a bunch of tall flat-head wood screws all in a column, proceeding away from the camera.
Camera must be dead-on at same height, level, and square to the target. Then go through taking 3-5 shots at each step in the AF Fine Adjustment menu (set to option 3, where it stores the adjustment for each lens). View the shots on a large monitor.
This also works well, with the long ruler, and the software, and is time consuming but nails it. It costs more, but is a fraction of the price of your lens:
LensAlign
I had the competing one, and it did not work as well.
Another option that works for some folks is to print a Bob Atkins photo test chart from his website, and stick on a wall. Then use it as a test target, but I found this did not too well.
Some folks use the Dot Tune method.
I haven't tried it, but it looks like it is less time consuming.
Other things
- if you wear glasses/contacts, get your eyes checked, get your prescription up to date, play with the diopter dial on the viewfinder. One click in either direction can make all the difference.
- don't try to check focus on the camera LCD panel. Download to a PC and scrutinize there.