Serve without being conspicuous. Serve silently without any advertisement. Without belief in God, without belief in an ordered world you cannot live amicably; you cannot work for the community.
Do what is right and leave the results to look after themselves. Do your duty with more and more confidence in the Lord. Become a lover of humanity. Foster kinship with all humanity.
Feel that the one Lord dwells in all. Feel that it is he who gives you an opportunity to serve him through all suffering mankind. The world is more and more in need of karma yogis.
Humanity is your God and service to humanity is your worship. Self-control is a natural corollary to the spirit of love and service. He who works with his mind detached and free from selfish longings is a real sanyasin.
The spirit of selflessness is the key to success in the yoga of action. Service becomes karma yoga to the extent one practises self-control and self-denial. With all actions done without expectation of reward, you will gradually become satvic (pure). For one who has faith in God, karma yoga becomes easy and purification of the heart is quickly achieved.
Knowledge of Atman (Self) dawns in that pure mind which is purified by selfless service and devotion to the Lord. When the yogi feels he gets all his power from the Lord - then the 'doership' ego will go.
Selfless service must be based on sadhana (spiritual practice). You must be regular in your prayers, your meditation, in the repetition of the Lord's name, in enquiry and self-analysis. All these are the inner springs of the right spiritual bhava (attitude), which is essential to karma yoga.