Sathigur kee saevaa safal hai jae ko karae chith laae
Fruitful is service to the True Guru, if one does so with a sincere mind
All the Gurus showed us how to do seva correctly from Guru Nanak Dev Ji to Guru Arjan Dev Ji for example feeding the hungry and Guru Amardass Jis seva of ishnaan. Guru Arjan Dev Ji writing the Shabad Guru Shri Guru Granth Sahib Maharaj this was service for the benifit of others. Guru Hargobind Ji to Guru Gobind Singh a great amount of seva was done Guru Har Rai Ji built hospitals for the sick, Guru Harkrishan Sahib Ji going through Cities and Towns healing the sick. Guru Tegh Bhadar Ji giving his head for the Hindus this was selfless service to keep the Hindu faith going so all the Hindus were not converted.
Other examples of Serving Humanity in sikhi are Bhai Khanaiya Ji is a great example; he gave water and first aid to everyone in the battle feild not creating divsions if they were low caste or high caste or if they were Muslims or Sikhs that is Serving Humanity. Another example of Seva is Bhagat Puran Singh who set up the world famous Pinglewara helping the poor, disabled young children up to old aged men and women. Seva is somehting you do by hand like Bhagat Puran Singh who founded Pingalwara by doing Seva himself of the poor and sick.
Sathagur kee saevaa gaakharree sir dheejai aap gavaae
It is very difficult to serve the True Guru. Surrender your head; give up your selfishness
I think that the Sikh panth is is not doing as much seva as it could we should try and play our part and do as much seva we could, look at our history to get more inspiration on how and where to do Seva and what Seva is. Seva in the mordern world is being done by Khalsa Aid and United Sikhs who go to the scenes of natural disasters and they supply food water and shettle and rebuild peoples homes that were demolished by the natural disasters.