Piece for solo cello

No - it doesn't go like that. The cello is a wysiwyg (what you see is what you get) instrument with clefs. You could be confusing yourself with the bass - that sounds an octave lower than written. As regards clefs, you can jump to anyone you like, there's no progression - well, that's what I say anyway!

Have printed it off and am off to play through it. Bit confused about the harmonics but will work through it anyway.

Yep, Thomas is correct about the clefs.

Thomas, the harmonics are easier than they look. You simply play where the notes are written, but some of them sound a different note.^^

Managed to figure that out afterwards. Love the beginning, and the progression in the first few bars. Harmonics are great, just getting them to play is another thing ... I'm such an amateur!

The middle section, where you've placed the tenor clef, I don't think it's necessary actually. You're not going extremely high and the phrase pattern is repeated so I'd suggest just keeping it to the bass. I was a bit confused about the crosses (+). I take it they mean stopped tones. This B section can get a bit boring but it does have potential and character. Maybe a new chord sequence could move it somewhere else, or just add dynamics.

In Bar 9, how about making some sort of chordal sequence, just to bring the piece to some sort of finale? As I was playing through, I always found I had a weird gap between pizzing the last note of Bar 9 and going to play the harmonic in the next bar. It was just having to stop strings from vibrating to get to the harmonic - maybe you could use something else.

I think the D.C. is fine.

The little crosses actually mean left-hand pizz on the notes they're over.

Thanks for all the suggestions!