From time to time, you will probably incur expenses personally, whether by credit card, cash or out of your own personal bank account.
To claim these costs back from the company, you should fill out an expense claim, usually on a monthly basis, to be checked by the company board and then reimbursed to you.
These expenses should then be declared to HMRC on form P11d each year, and genuine business expenses can be reclaimed from HMRC using form P87.
Fortunately, you can makes things a lot easier for yourself - get a dispensation from HMRC so you do not need to report most of your expenses on the annual P11d.
This will usually cover such things as travel, subsistence, professional subscriptions, telephone costs etc, which should then remove the requirement for you to complete P11ds and ancillary paperwork.