Here's a thought:- Experiment. Play around with a few scales in C, see what works. Try not to think about it too hard or it'll become too much like an excercise, let it flow from under your fingers. If you're new to soloing it is most likely to sound absolute rubbish, but skill comes with practise and soloing is just another skill.
The answer the theory side of your question, you could actaully just solo using either C Major and Am (Pentatonic optional). If you've discovered modes yet you could also use G Mixolodian and F Lydian; however if that's just confuessed you, stick with Am or C. Most rock guitarists find it easier to solo using the minor scale, probably because of the finger postioning. Anywho, no doubt I've just confuessed you even more. Good luck and feel free to ask any questions.