(If you want to go directly to summoning an entity to aid you - skip this section and go directly to section 13 onwards).
Now the most important point you must remember is "Why are you summoning the Entity?". One of the main reasons to summon a negative entity is to use their natural negative energy and direct it to an enemy or group of enemies.
Pretas, Bhoots, Asuras, Rakshasas exist in negative planes (or Talas) and as such are saturated with negative energy. They also feed off negative energy so can superficially leech off your negativity to grant you 'positive' wishes in your current life such as wealth, power and other low level vices. (Note: To deeply remove negative energy in order to break the Karmic debts and dispel true negativity you need Aaiyyan Stones or a High level Hindu Aaiyyanist healer - but that is outside the scope of this book).
There needs to be some clarification here. In Hindu Aaiyyanism Pretas, Asuras, Bhoots etc.. are negative entities. Some people may also refer to the as 'Evil Entities', but as Hindu Aaiyyanists we cannot condemn nor condone the actions of others (human or non human). Historically, entities that exist in Talas were beings who were negative/evil when they existed in our realm (i.e. when they were alive or existed in this world many thousands of years ago). However, we are all part of Brahman and so should respect and love all entities as 'One' no matter what their actions were.