Hey Slapin,
From the context it sounds like you're trying to transition through different anim states to create a full loop. So I'm assuming this is for a video game?
First bit of advise, animation is animation no matter the context it's being used. All of it follows the 12 principles of animation. Get comfortable with them. Practice them. Love them and they will love back. :) You're saying your punches don't feel like they have any force behind them and that tells me you're not using one or a combination of those principles. Go through the Animation Boot Camp. There you will learn how to apply weight to your objects and then work your way up to a walk cycle. ;) After that hit up the Animation Workflow and Body Mechanics. In that one you're going to learn workflows to observe actions and then animate them so they "feel" real. The instructor Wayne Dixon is a great animator and he's done an amazing job thus far to comment and provide feedback on everyone's exercises from his courses. This is where I recommend you start.
But hey, I've never seen your work. So maybe you've got these skills and I'm barking up the wrong tree. Okay cool! Here are some pointers.
For the walk cycle, if there are things you need to focus on (like in your case foot sliding) go simple and only have 2 animations. An Idle (standing still) and your main walk. Then when creating your main walk, start in the passing position (when the back foot passes the lead foot). By doing it this way in a game engine you are almost getting your "start of walk" anim for free. Doesn't work all the time but for practice and trouble shooting it should work well.
To fix your foot sliding problem, really take some time in the animation boot camp to learn those walks. Personally I still have issues with foot slipping and to fix it I like to animate the character actually moving forward. This way I know the steps are correct and planted. When I'm done I just remove the animation that is pushing him forward and you'll have a perfect treadmill walk cycle for your game.
For your punch animations I would say reference reference reference! Not just real life either, if this is for a game, take a look at your favorite fighting game and study that as well (specifically the timing). Take a look at this site: The Animator's Resource Kit . This site is full of great places to go for reference and other great animation goodies. :) Also, do yourself a favor and watch THIS video by Jason Shum. He is a terrific animator and it goes through his thoughts on the key poses you need for a great combat cycle.
Finally I want to leave you with this bit of advise. Don't be afraid to show your work and get critiques! It is absolutely essential to getting better at animation. Getting valuable feedback by posting online can be hard at times and it will leave you feeling vulnerable but your work will benefit from it. Remember critiques are never personal they are meant to build you up to being the best you can be. So show us what you got! :)
I'm an animation student like you discovering what it takes to create realistic movement and bringing characters to life. This is all based on my experiences. I hope some of this is helpful to you. Happy animating!
Thank you so much for the pointers! I think I better go again about Animation Boot Camp videos.
I tried the approach to animate actual walking then removing forward animation, the problem is the same as I can't get feet speed constant (when touching ground) and linear, thus sliding occurs. So I wonder how I should set up my workflow to produce walk loop so that it is not sliding, would like to see how masters do it... I never seen video where the mechanics would be explained regarding this. And yes, that is for game. I just learn and use Makehuman characters for animation so I do not share so no unhealthy questions asked (I can model and rig, but I fail in persistence - I lose motivation completely after mid-rigging and have lots of incomplete characters, so I decided to drop a matter for a few years and concentrate on things I like - coding and animating).