This is a ritual that I have used in the past when I felt the need to contact a departed soul. It is quite a bit like most invocations. It is important to maintain a 'containment' space for what you summon. This is because things masquerading as the person whose spirit you are attempting to contact will arrive sometimes. Not all of these false spirits are benevolent towards those who performed the invocation. In fact, there's a good likelihood that the spirit is not kindly towards people who perform summonings. This is where the stories of haunted Ouija boards start.
As much as I abhor the concept of 'cook book witchcraft' I find that laying out the steps and process of doing a spell like a recipe works out really well. I ask that you forgive my brief foray into the Martha Stewart of occult world for the sake of easier to read format.
Item with strong association with the soul you wish to contact
Method to light candle
Divination tool of choice (I like tarot cards for this purpose.)
1. Make a circle with your salt. As you do so, envision a sphere of power being built with the level you are on being the center. You may wish to invoke guardian spirits to make the circle of power such that anything summoned can not exit it with out your command.
2. Rub the candle with the item you associate with the soul you wish to contact. As you do so, envision some of that person's essence being imparted into the candle.
3. Place the candle in the center of the circle.
4. Intone the following: [person's name] I summon you from eternal repose. Come forth, come forth, come forth.
5. While chanting the above, light the candle.
6. Inform the soul you summoned that you wish to speak with them. Hold up your divination tool. Inform them that this is the method they can use to reply to you.
7. Ask 3 simple yes/no questions that has a decided answer which you know. Check your divination tool to establish what is a positive and a negative response.
8. Method of communication established and clarified, proceed to your questions, comments, or concerns that you wish to discuss.
9. When finished with your discussion, intone the following: [person's name] I return you to eternal repose. Go back, go back, go back.
10. Extinguish the candle. Sweep up your salt and throw it away. Return your divination tool to a 'neutral' state and ground yourself.