Carefully consider the timing of your application. You can submit your application up to 28 days before you reach the qualifying period and you can also start the qualifying period from the date you were granted entry clearance, provided you count the time between the grant of entry clearance and arrival in the UK towards your total absences.
If you are unsure about when to apply, it is always best to take legal advice as your application can be rejected if it is made too early.
Once you are aware of the date you intend to apply, you should ensure you pass the Life in the UK test in advance of this date. So plan your revision early!