Any day now you will receive you’re licence renewal and D4 medical form if not soon then contact the DVLA.
Firstly go and get some photos done Max Speilmann do them for £7 for 4 not cheap but they crosscheck the picture online so it meets requirements for passport and driving licences, I’m sure other companies do the same.
Next book an eye test and a medical and take the D4 with you to the eye test as there is a section for the optometrist to fill in and a box for them to stamp.
Next take the medical and make sure you proof reed and check carefully that both forms are correctly filled in, then send both forms off together (there is no fee)
and wait, my licence took about 3 days to come back I wouldnt recommend leaving it too late if you even sign you’re signature outside the box they can send the form back causing further delay.
Get receipts, even if you have to pay yourself you are entitled to tax relief for expenses relating to you’re work.