Section 1. Tanar'ri
Bebiliths: A spider like demon that hunts and kills other demons. I cant tell you how many times its helped me when summoning to have a bebilith nearby. Prior to summoning a demon, have a bebilith on hand. They're always eager to have a chance to hunt demons, so its fairly easy to have one on hand in case things go bad. Making friends with one is a good thing too.
Prior knowledge: Not only is it good to know what type of demon to summon, names, background, allies and enemies, and affiliation are excellent to have on hand. Knowing enemies is extremly important as demons like any opprutunity to wreak vengaence on those who have wronged them.
Appetizers: Distasteful, I admit, but it is helpful to have servings of intelligent creatures to quench a demon's hunger for vileness. Children's blood is a rare commodity in the lower planes and serving it is a sure way to get a demon on your side.
Fear: from the lowliest dretch to Demogorgon himself, fear is the one thing that will rule. When summoning lesser beasts (and always make sure lesser)
fear will suppress them. Have weapons that look, and hopefully feel, painful. It's good to have minions on hand (I prefer undead, but anything will work) to give them a sense of how much opposition they'll have in things turn ugly.
Modesty: More so with greater demons, keep your more powerful items and minions hidden as to make the demon think you less of a threat. Yet dont be too modest, as an easy kill is a game to any demon.
Flattery: Flatter them with any form of compliment you can think of. All but succubi or mariliths will prefer comments about they're might, power, strength and ability to cause terror instead of looks or anything like that.
Section 2: Baatezu
Generrally, things from section one apply to devils.
Association: On the average, devils from one layer of hell are going to work with mortals associated with that same layer. Yet seeing how politics in hell are filled with rivalry, make sure who you summon is not an enemy of whichever layer you are associated with.
Divination: Devils like to use trickery, cunning and deceit as weapons, so using divination to make sure youre not being tricked. Keeping a careful watch on what hes doing is key to your success. Be careful for illusions and invisibility in case he attempts to escape.
Bargaining: Bargaining is essential when dealing with devils as they often prefer to use cunning and respect those who use their methods. Diplomacy is an excellent skill and a mixture of timing, bargaining, and a good deal of bribery will be of incredible help when dealing with devils.
Pecking order: establish a pecking order between you, your devil and his servants, and your own minions. It's best to put the devil next to you and have him take care of his own servants with your own. be careful with your own servants if you lessen them, as treachery might occur if you're not careful.
On a general note: help is a good thing. here are some summoners who will give a hand to those with gold:
Demon Driver
NE half-fiend wiz/ach/dev 20/5/5)Cali****e wizard. He resides in Memnon and is affiliated with a group dedicated to the Hag Countess. He knows mostly about demons, but will aid with whatever problem you have in exchange for gold.Nazadath Hizzildeth
CE drow div/lor 20/10) archmage of Schindilryn and as unpredictable as the demons he summons. He possesses a multitude of powerful items. At the price of any bizzare thing or gold. He loves creating bizzare things so it is essential you don not wind up as one of his servantsThus ends my guide. Long yes. but devils and demons require length to explain their intracities.