This is a long pending question. What is Vyasa Poornima/ Guru Poornima Puja.
We have to understand the difference between the Guru Puja and Guru Purnima Puja first. Guru Puja, nor mally in south, is one celebrated on the day of the Samadhi of the Guru, otherwise called as Varshika. Whereas, Guru Purnima Puja is celeberated for the Gurus in the Sampradaya / Parampara / Tradition.
This is normally celebrated by the Sannyasins. This is also an important day, as it is the day of the beginning of the Chaturmasya. (See – Chaturmasya Nirnaya page in the blog). We should remember, the puja a parahamsa sannyasi performs on this day too, is only Manasa Puja or Mental worship and not a Physical worship.
In this five peoples belonging to five groups are worshipped along with ones own, Guru parampara.
Firstly, in the Center of all the group, Lord Krishna, who is nothing but the Paramathman (Self) himself and Jagat Guru, is worshiped. Around him are worshiped the other forms of Sri Krishna, Sri Vasudeva, Sri Sankarshana Sri Pradyumna and Sri Aniruddha, are worshipped. The position is Sri Vasudeva in the left top, Sri Sankarshana in the right top, Sri Pradyumna in the right bottom and Sri Aniruddha in the left bottom.
Then, in the right side of Sri Krishna, Sri Vyasa Maharishi is worshiped. Around him are worshiped his four maharishi disciples, Sri Sumanthu, Sri Jaimini, Sri Vaisampayana and Sri Paila. In the same order as previous (LT, RT, RB and LB).
To the left of Sri Krishna, Bhagawan Bhashyakara Sri Shankaracharya. Around him are worshiped his four disciples, Sri Padmapadacharya, Sri Sureshwaracharya, Sri Thotakacharya and Sri Hastamalakacharya.
Above Sri Krishna, Devarishi Sri Sanaka is worshiped. Around him, Sri Sanandana, Sri Sanatana, Sri Sanatsujata and Sri Sanatkumar.
Below Sri Krishna, Sri Dravidacharya is worhiped. Around him, Sri Gowdapadacharya, Sri Govindacharya, Sri Vivaranacharya and Sri Sankshepakacharya (Sri Sarvagatma muni).
In front of all these people, Sri Guru is worshipped alongwith, Parama Guru, Paramshti Guru, Parapara Guru should be wordhiped. Since we have already worshiped Sri Krishna, Maha Guru worship is already done. Here, we can worship all the other Acharyas of Brahmavidya, like, Sri Vacaspati mishra, Sri Vidyaranya, Sri Madhusudhana Saraswati, Sri Sadhashiva Brahmendra, Sri Appayya Dikshitendra, Sri Chandrashekara Bharati, Sri Chandrashekarendra Saraswati and other Acharyas one has great respect for.
Around these group in the eight corners we should worship, Indra etc. devatas, as worshipped in a Yantra or Mandala.
It is a day for the disciples to worship their Guru. Guru too, himself being a disciple of some Guru, worships him.