Im fond of MN 131: Bhaddekaratta Sutta http://www.accesstoinsight.org/tipitaka ... .nana.html
Let one not trace back the past
Or yearn for the future-yet-to-come.
That which is past is left behind
Unattained is the "yet-to-come."
But that which is present he discerns —
With insight as and when it comes.
The Immovable — the-non-irritable.
In that state should the wise one grow
Today itself should one bestir
Tomorrow death may come — who knows?
For no bargain can we strike With Death
who has his mighty hosts.
But one who dwells thus ardently
By day, by night, untiringly
Him the Tranquil Sage has called
The Ideal Lover of Solitude.
In sitting meditation stay with that ‘which knows’ everything. Don’t try to go to objects. Let the objects come to you. Try not to react to objects. Whatever arises — greed, aversion, pain, itchiness, metta, likes or dislikes etc. — watch with equanimity, without getting involved, without clinging to it. Stay in the middle path.- Shwe Oo Min Sayadaw