I have problems drawing a 2d walking/running stick figure animation for my game.

I noticed this is a problem of a lot of games made decades ago but still today many games lack of proper walking animation even with 3d bone-animations (don't know how to call them).

Tried a few tutorials on drawing this looking natural and even a stick figure software where you can adjust the limbs.

Has anyone any tips?

Honestly, just google "walkcycle". Or maybe "4 frame walkcycle" or 6 or 8 frames or whatever you're shooting for.

If indeed you're drawing your own figures but you have no background in drawing, you can even just make a new layer and draw your own walking figure overtop of a tutorial image you find online. If you do have drawing skills, you can use that as a base and modify from there.

Just taking a glance at the first page of google hits tells me there are lots of good tutorials that explain the details that go into selling a believable walkcycle, so give 'em a read and try drawing one. Then do it again, better.

Better yet, if you want critique, post your animation frames here for people to have a look at.

I noticed this is a problem of a lot of games made decades ago but still today many games lack of proper walking animation even with 3d bone-animations (don't know how to call them).

This depends on your definition on "proper walking animation", in comparison no engine has "proper graphics" because there isn't one that renders the same quality as in in the real world.

I have seen a lot of bad walking animations in indie games, however if it doesn't brake the immersion it's fine.

Has anyone any tips?

Lift your knees and bent your toes, because no software has 1-1 animation translation you need to over express your animation; even "realistic" animations are over expressed; motion capture is edited after capture because computers are bad at using realistic animation data.

Realistic is overrated and time consuming, settle for believable animations over realistic.

Put some character in the animation, if the animation is telling a story people will focus on the story instead of the realism.

Walking is a complex animation, when you study animation it's taught in your third and last year. Attempting to make a walking animation without any animation knowledge is like learning to walk when you haven't even crawled yet.

If you want walking animations without years of practice then you need to hire someone who has learned what you need; hire an artist.

Get a copy of The Illusion of Life it's a good read even if you are not into animation.

Honestly, just google "walkcycle". Or maybe "4 frame walkcycle" or 6 or 8 frames or whatever you're shooting for.
If indeed you're drawing your own figures but you have no background in drawing, you can even just make a new layer and draw your own walking figure overtop of a tutorial image you find online. If you do have drawing skills, you can use that as a base and modify from there.
Just taking a glance at the first page of google hits tells me there are lots of good tutorials that explain the details that go into selling a believable walkcycle, so give 'em a read and try drawing one. Then do it again, better.
Better yet, if you want critique, post your animation frames here for people to have a look at.

Perfect! A matching google keyword saves a lot of lifetime. This is the last and best animation I made from what I have learned from your post in Paint.Net.
Suggestions?

(There is a serious bug in this new forum software, don't know why this image is so gigantic)
It's enough for prototyping for now. Now I need to make a running animation.

Realistic is overrated and time consuming, settle for believable animations over realistic.
Put some character in the animation, if the animation is telling a story people will focus on the story instead of the realism.
Walking is a complex animation, when you study animation it's thought in your third and last year. Attempting to make a walking animation without any animation knowledge is like learning to walk when you haven't even crawled yet.

"Believable" was the word I was looking for. My human-like character animations are not very believable. Most of my walking/running attempts didn't really made the stick figure look like they are moving but doing jumping jacks while hovering over the floor.
I realize now as well that this is a pretty complex theme. I was hoping that there was maybe an animation software that could prerender these complex, yet everyday animations in game dev.

Suggestions?

It's hard to see when a body part moves past the body because of the frame skip, maybe add a Fresnel line on the edge or a depth gradient to show what limbs are in back.

I realize now as well that this is a pretty complex theme. I was hoping that there was maybe an animation software that could prerender these complex, yet everyday animations in game dev.

Free pre-made animations are free because they where made as tests, there are lots to find scattered on the net. Paid animations are better although finding what you need is hard. Some universities give away free motion capture data, it's unclean although high quality.

Maximo that Norman suggested is great tool and is probably the nearest thing to a animation library that the world has.