I was virtually in the same position as you quite recently.
I part own my own house with my missus and I bought another house with a friend (50% share each).
Any repairs and maintenance to the house will count towards tax deductables when you sell the house so keep all your receipts etc. I'm not 100% sure if absolutely everything counts, for example, regular gardening work, or maybe even decorating, might not count, though I may be wrong.
When you sell, you'll both have your capital gain's allowance that you can offset against the profit as well.
I'm not too sure what the current CG allowance is - it's approx £10k, so if, for example, you pay £100k for your house and you have £10k of receipts and you sell it for £160k, you'll both have made a profit of £25k ..... minus your CG allowance of approx £10k - you'll both pay CP on £15k at the appropiate rate.