Sehaj comes through Guru Sahib's Kirpa and Kirpa comes through Naam and Gurbani. The 18th Pauri of Siri Anand Sahib is dedicated to Sehaj Avastha:
ਕਰਮੀ ਸਹਜੁ ਨ ਊਪਜੈ ਵਿਣੁ ਸਹਜੈ ਸਹਸਾ ਨ ਜਾਇ ॥
ਨਹ ਜਾਇ ਸਹਸਾ ਕਿਤੈ ਸੰਜਮਿ ਰਹੇ ਕਰਮ ਕਮਾਏ ॥
ਸਹਸੈ ਜੀਉ ਮਲੀਣੁ ਹੈ ਕਿਤੁ ਸੰਜਮਿ ਧੋਤਾ ਜਾਏ ॥
ਮੰਨੁ ਧੋਵਹੁ ਸਬਦਿ ਲਾਗਹੁ ਹਰਿ ਸਿਉ ਰਹਹੁ ਚਿਤੁ ਲਾਇ ॥
ਕਹੈ ਨਾਨਕੁ ਗੁਰ ਪਰਸਾਦੀ ਸਹਜੁ ਉਪਜੈ ਇਹੁ ਸਹਸਾ ਇਵ ਜਾਇ ॥੧੮॥
(The Sehaj Avastha does not come as a result of Trai-gunni Karma and without Sehaj the doubt (Sahsa) does not go away. The Doubt does not go away through any worldly means, no matter one may get tired of doing these means (karma). Because of this doubt (Dubidha or Sahsa), the mind is impure, then how should the mind be washed of its dirt? Wash the mind by engaging in Shabad, stay focussed on Hari Vaheguru. Siri Guru jee says, Sahaj comes through Guru Sahib's Kirpa and then this doubt (dubidha) goes away.)
Basically, we would have live our life according to Gurmat which means that we would have to keep Rehit, get up at Amritvela and stay engaged in as much Naam and Gurbani Paath as possible. This would ensure that through Guru Sahib's kirpa, Sehaj avastha comes to us.