What William MG said about practise and time, but as a general tip try to observe and analyse for yourself what is occurring with your playing, and do it with every fretting/fingering issue you encounter in future.
Specifically in the case of open C. Here's what I've discovered along the way on my journey so far.
From the beginning, personally I've always found open C an easy chord, but observed these idiosyncrasies specific and general addressing things which have facilitated its playing and optimised the consistency of the tone of mine -and other chords, over time.
To finger it best Open C requires a consciencious awareness to stretch to optimise each finger's placement relative to its fret position until the action becomes subliminal. The closer to the fret, the lighter the required pressure will be (important as you will see in a moment) and generally, the cleaner the note and truer its tone. Concurrently, with thumb in optimum supporting position mid neck [u]hand position should be curled lightly about and around the neck[/u] permitting you to keep each fingertip as perpendicular to its respective string as possible, more difficult always with stretchy chords. Keep trying. Over time, it'll happen.[br][br]Things which can render this more difficult.
[u]Fingers[/u]. Do you have spider, average or fleshy shaped fingers and tips? Fleshy which are usually broader by association will compress more and spread as we tend to apply higher fretting pressure.
[u]Fingernails[/u]. Too long and a nail may touch the fretboard before the tip which in turn provokes appyling even more pressure to fret the note which exacerbates tip spread which can partially or fully mute an adjacent string, exacerbated by finger tip angle to the string. Like the three basic body types and shapes, we have difference shaped tips along with how our nails grow or protrude from them too. Ectos seem generally to be blessed with nails which are recessed from the narrower bonier tip naturally, endos more frequently the nails protrude over the tips requiring nails to be regularly and well trimmed. Little things, but they do make a difference. The devil is in the detail.
[u]The guitar[/u]. String spacing, neck profile, scale length, action, string gauge all make a difference to how far you will have to stretch and pressure you will have to apply. Radius counts too, but is usually more consistent across brands with acoustic if that's what you're playing than with electric IMO&E. Is your guitar a good fit for you?
