Don't be late with declaring your VAT and paying it. You must do this before the end of the month following the quarter. That means

BTW deadlines

The first quarter runs from January to March, the deadline is 30 April. 

The second quarter runs from April to June, the deadline is 31 July.

The third quarter runs from July to September, the deadline is 31 October.

The fourth quarter runs from October to December, the deadline is 31 January.