As my dad’s not overly astute in the financial management side of things, I agreed that I would help him out in that respect. I’m a year 11 Accounting student so we’ve covered most of small business bookkeeping. I’m just wondering which accounting method would be most appropriate (and which software).

The business I only likely (at present) to consist wholly of himself (service business). I would probably be listed as an employee in these circumstances though.

Most small business cease to exist within a year which is usually good for tax avoidance, therefore I would say that minimium accounting should be required – probably the easiest and most understandable would be to build you own using the most well known Spread Sheet program (which I think most people already have loaded in their PC or laptop).
Cash flow is essential to monitor and you could plot some easy to read graphs to show progress – often more revealing than a columns of figures or pages of accounts.