In order........
1. Ammunition.
Since all guns are individuals, what works great in my gun may choke your gun.
So, the best answer is to select a brand/type of ammo and test fire it.
If it fails, try another until you find one that works.
This is especially critical in a defense gun.
2. Magazines.
The factory mags tend to work best.
Keep the magazines clean.
3. Lubrication.
The Walther's seem to "like" slightly heavier amounts of liquid lubricants, and tend to love a good grease.
Use grease on the outside of the barrel, the outside of the recoil spring, the slide and frame rails, the sear where it contacts the hammer in double and single action, and the end of the draw bar where it contacts the sear on the right side of the frame.
4. DA trigger pull.
The DA trigger on the Walther's is heavy and there's not much that can be done about it.
No one has ever managed to put that many features in that small a pistol and the trade off is the heavy DA trigger pull.
The problem is that Walther squeezed a lot into a then-tiny frame, and the DA pull is a matter of leverage.
You could install a lighter mainspring, BUT that very often causes miss-fires and other stoppages.
What to do is simply use the gun and get used to the trigger. After you get used to it and strengthen your trigger finger, you actually stop noticing the heavy pull if you use it enough.
Some fun can be had by handing your Walther to someone unfamiliar with them and having him shoot it.
Often you can watch as they pull and pull, then ask if the safety is on.
The Walther PP series of pistols are sort of the 1911 of small autos.
It's the .32/.380 that all other .32/.380's were judged by and very few were ever able to rise to the Walther level.