If you claim either working tax credits or child tax credit, you need to renew your claim. For the year to 5 April 2012, you will need to confirm your household income. The deadline for renewal is 31 July 2012, although if you are self employed, you may give estimate figures and then give actual figures by 31 January 2013.
If you are self employed, you need to declare your taxable profit, not your accounting profit (which may differ depending upon your circumstances).
If you are a company director, you need to declare your salary and dividend income. The dividend figure is the gross dividend, i.e. the amount of dividend paid plus the tax credit attached to that dividend. It should be reported as investment income.
As your 2013 award will be based on the actual figures for the year to 5 April 2012, it makes sense to renew sooner rather than later, to avoid a situation where you are overpaid tax credits.
The tax credit renewal helpline is 0345 300 3900. Further information is available here.