Meditation is a process of letting go, so you don’t have to exert any more effort that the effort to let go.
You don’t need (or indeed want) to exert effort to hold onto a meditation object like the breath for example.
I’ve just looked it up and Ajahn Brahm’s method starts with ‘sustained attention on the present moment’, which is the same as letting go of the past and the future. So exert just enough effort in this stage to let go of the past and the future. This means that you need to recognise when your mind starts thinking thoughts of the past or thoughts of the future. Once you recognise them they will usually stop all by themselves. Then you can rest effortlessly in the present.
Don’t attempt to move into a deeper level (stage in Ajahn Brahms parlance) without establishing yourself where you are for a sustained period of time.
Ajahn Brahm talks about effort in the opening of the basic method of meditation.