1) NEVER attempt to force an entity to do your bidding, unless you have a death wish.
2) It isn't possible to become a demon through a spell, despite what anyone on this site says.
3) If an entity doesn't appear the first time you try to summon it, assume it doesn't want to be messed with and wait 2+ months before attempting to summon him/her again.
4) Don't say stupid things, for example, "I command you," "I am now your master," etc. Always be respectful and courteous, f.e., "My lord," "My lady," "Dearest ______" If you are summoning the spirit of someone you knew personally when the were alive, it's fine to use nick names as long as they aren't offensive.
5) Do your homework! You can't just summon a random demon. Look up and memorize some demons and consider the best way to get their attention. (Certain demons might prefer jewels, food, precious metals, etc.)
6) NEVER, EVER TRY TO SUMMON LUCIFER!!!
7) Don't use your own blood if you're doing a blood ritual. Animal blood works just as well.
8) Make sure the area you are going to use to summon an entity is free of religious articles.
9) There is no such thing as summoning a so-called 'Dark Angel.' This is a generic name for a demon.
10) It isn't possible to have a spirit guide, teacher, soulmate, etc that is a demon.