Here are 6 things you should avoid in order to protect your score:
1) Paying utility bills late
2) Forgetting to pay your rent (you'll probably get away with this, unless your landlord takes you to court)
3) Reducing income - for example, if you are made redundant or go part-time
4) Repeatedly increasing your credit card limit
5) Failing to pay a small-time vendor - unlikely to be reported by the vendor themselves, buf if they factor the debt or pass it on to a debt-collection agency, you will probably be issued with a black mark...
6) Not paying your credit card balance
Point 6 is the most common problem today.
Moderate use of credit cards and paying them off each month is the best defence against a poor credit score.
Also consider improving communication - if you can't pay your lender, try to negotiate a payment break or just paying interest for a month or two - without them reporting you!