You can start by not copying Guts and Griffit but making ur own characters.
-Ok, so lets begin (if u dont like harsh crits dont read, but if you want help then read)
-First the heads ....
-The chin should end with the start of the ear. If you dont beleave me, wach naruto all over again and see
. The whole point is his ear is correctly in ratio to the eye and mouth, but it should be more to the right (our right) cuz of the jaw. Either that or short out the jaw.
-The head is too upright for that atack. His head and shoulders would have to be much more bent forward to concentrate mass at the sword. Its all the necks fault, and by Photoshoping it a little you can improve the effect, or just redrawing the whole head wich is silly.
-His mouth is too ill defined. You should spend more time on detail.
-Torso -
-The shirt should be wavering backwards, since he is making a fast move forward.
-Tho he was only what 15? when he battleed griffit for the first time, i beleave his arms werent so thin, but a lot stronger. Also there are some unneded lines on em.
-The hands seem a bit small, and could definetly use more defining. More detail on ea finger, more flexing of the skin and stuff like that.
-Hmm, used a ruler for the sword? i beleave the sword had a bit more detail... or stuff like that.
-His legs are a tad too short, and are pretty much not there, since it looks like (thanks to the folds) that he doesnt have a knee but emty space and air in em. Since he was moving forward, the knee would be pretty much defined, and its very baggy there.
-One of the legs has a violent decrease that doesnt look right, while the other foot is wavering about like he doesnt care if he even dodges the attack.
Ok nuf about guts, now its Griffit time ...
-You spent a lot less time on him, his hair should be longer and much better defined, his face doesnt remind me of griffit, and before i continue Berserk is a more realistic manga than the regular manga you see around. You shouldnt have attemted to draw it in the first place.
-The sword is curved wrong, and ends in a violent tip, while it had the same proportion untill the last decimeter in the manga. Also the blade is a bit in a wrong angle compared to the handle.
-The other hand is rely ill looking, and could do more work. At the same time, its unneded so who gives a fudge?
-Once again the folds are wrong, and he is wearing ... chinese slippers??? XD ...
Anyways, needs more work and you didnt give the work nuf time. Beauty is in the details, remeber that. Details can sometimes hide mistakes, and give a much better impression.