This was originally written as a Do It Yourself guide. I believe that it can be accomplished by a  skilled hobbyist. However not everyone is comfortable working on their firearm so I now offer the Reliability Preparation service.

This guide reflects tools and methods readily available to the DIY hobbyist, it does NOT reflect the exact tools and methods I use in my shop. It does however provide an excellent insight into what is involved in the Reliability Preparation.
 

Caution: Aluminum and polymer parts of a pistol are very soft and easy to damage. Do not sand or polish them unless it is to address a specific problem you have identified. It is extremely easy to get carried away and remove too much metal, especially when using a Dremel tool. Don't let this happen to you! Not all pistols will exhibit wear in all the areas indicated, They are places to check, and should only be addressed if signs of interference are observed.

Required are firearm cleaning supplies, firearm lubricant, common hand tools (hammer, punches, drill bits), some 400 - 600 (up to 1000) grit sandpaper and a couple hours of your time. A Dremel type tool with a felt bullet and polishing compound is recommended for putting a final polish on the feed ramp.

Items marked with an asterisk * are the most critical.

Field strip your pistol and clean off all the lubricant that is on it. (so it doesn't contaminate your sandpaper)

*1. Use a small piece of sandpaper folded over for thickness and drag it through the rails in both sides of the slide. The first few drags will remove some finish and you can see the rough marks left by the milling process. drag the paper through a few more time, you should be able to feel how much smoother it pulls through. Be sure to make contact between the paper and all three sides of the channel before you are done. It is not necessary to completely remove the mill marks, especially if they are deep, you just want to make them smoother to glide across.

*2. Sand the hammer interface using the sandpaper. Be sure to always finish your polishing going in the direction of contact.

3. Sand to smooth the breech face. be careful not to damage the extractor. (remove extractor first if you intend address the extractor- step 13)

4. Polish the inside of the opening that the barrel passes through. Again go in the direction the parts move.

5abc. Use the sandpaper to gently dull the sharp edges on the slide that contact other parts.

6. Sand the flat areas inside the slide that contact the barrel when the slide retracts. Don't try to remove the machine marks, just smooth it a bit.

Remove the allen screw on the top of your slide that retains your firing pin. Be careful, the pin is spring loaded and will shoot out the rear of the slide with force if you do not contain it. (In later models, this is the screw that holds the extraxtor)

7. Polish the surface of the firing pin stroking lengthwise, in the direction of travel. DO NOT sharpen the point of the firing pin.

8. Polish the flat spot on the rear of the pin. It does not have to be perfectly smooth, just take off the rough edges.

9.. Polish the outside of the firing pin spring lengthwise.

10. Lightly polish the bottom of the set screw where it would contact the firing pin.

11. no pic. Using a drill bit the size of the firing pin hole (on the breech face side) work it in and out of the firing pin hole a few times by hand to deburr it.

12. no pic. Using a drill bit a few sizes larger than the firing pin hole, lightly chamfer the firing pin hole on the breech face side. This will make it more difficult for debris and grime to build up.

Reinstall in the reverse order. The firing pin goes in with the flat part toward the screw. tighten the screw down until it just touches the firing pin, then back it out one half turn..(on models with the screw holding the extractor, you can tighten the screw down all the way) Verify that the firing pin moves freely.

Using the appropriate size punch and a solid surface, drive out the roll pin holding in the extractor. It is under spring pressure, so contain it. (on later models the extractor is held in with an allen screw)

13. Lay a piece of sandpaper on a flat surface (glass). lay the extractor on the sandpaper and polish both sides lightly by sliding it around on the paper. This ensures an even, flat sanding You don't have to polish the entire surface, just take of the rough edges. Do not change the shape of the claw that engages the case rim.

Do not polish the roll pin. You want it to be a tight fit that will not fall out.
 

*14. Sand the feed ramp. The goal is to reduce or remove ridges and pits, but no metal after that. Roll up a piece of 400 grit sandpaper, or wrap a piece around the end of an eraser and work the sandpaper up and down the ramp, the way the bullet moves. You can over do this, especially in the middle, so make sure not to alter the shape of the feed ramp. If you want to do a real good job, go over it again with 600 grit sandpaper, or polish with a Dremel.

*15. Sand the chamber, the area inside the barrel just past the feed ramp. I find it easiest if you roll up some sandpaper. put it inside the chamber and then allow it to unwind to the size of the chamber. Sand by sliding it in and out, not rotating. (polish in the direction of movement)

16. Sand inside of the lug. This time use rotation to polish since that is the direction of movement. Be careful not to change the shape.

17. Use a wooden dowel to push a few strands of a stainless steel pot scrubber (see pic below) through the barrel from the feed ramp side. Repeat a few times. The wad of pot scrubber should fit tight so it will smooth the machining marks inside the barrel. (this serves the same purpose as lapping, or fire lapping the bore)

18. Sand the outer surface of the barrel, especially the belled portion, avoid the muzzle opening. (do not round the edges)

19.  Lightly polish the guide rod using lengthwise strokes. I recommend replacing the polymer rod when it becomes bent.

20. Lightly sand the outer surface of the recoil springs, lengthwise.

21. Sand the takedown pin by wrapping the paper around it and giving it a few turns.

22. Sand the inner radius of the guide rod hole by using an in and out motion. On most pistols this will be part of the slide.

23. Sand any sharp edges that may drag on the frame. On many pistols this area will be part of the slide.

This is a good place to stop and enjoy the major benefits of the Reliability Preparation. However the next steps further reduce friction and increase reliability with added benefit of smoothing the trigger pull.

The slide stop / ejector and trigger bar are stamped steel. As such they have one side where the edges are sharp and need special attention

1. Using sandpaper on a flat surface (glass), polish the slide stop / ejector. Just take off any sharp edges.

2. Polish the slide stop / ejector spring, paying special attention to the ends.

3. Polish the trigger bar, using the sandpaper on a flat surface method. Do not change the shape of the tab that engages the hammer.

4. Polish the edges of the hammer using sandpaper on a flat surface. This is a good time to polish the hammer face again.

5. Lightly polish the hammer pin.

6. Do not polish the aluminum frame.

Reminder, do not sand or polish the rails on the aluminum frame that is mounted in the grip. You may carefully remove any burrs that have formed from use, but be careful to remove no more of the anodizing than is necessary.

*7. Polish the hammer face.

8. Smooth any machining burrs on the takedown pin holes that may interfere with the movement of the barrel.

9. Relieve and smooth the front edge of the frame where the springs drag when they compress.

10. If your barrel has been gouging the frame as in the picture, you need to sand the area just enough to eliminate the contact. Or sand the barrel to eliminate the contact and just smooth the frame.

11. Smooth the front edge of the grip where the nose of the slide extends past it. This is not required on all pistols, check to see if the slide contacts when retracted.

12. If you see scuffs where you slide has been dragging on the frame support, gently sand a little to eliminate the contact.

13. Check the slide catch to see if it drags on the bullets or the side of the magazine follower causing a premature lock back of the slide. If it does, sand it down, just enough so that it no longer drags.

Thoroughly clean all parts, lubricate as normal and reassemble.