Sissifying a beta male

Sissifying a beta male is not about making him feel sexually attracted to you - most beta males don't feel attracted to men in this way at all. When a sissy allows a man to fuck him, it is not out of sexual attraction, but obedience. For the sissy, it is about giving up control to a superior man. To acquire control, you must gradually make him feel small, weak, and emasculated in contrast to you. At the same time, you must appear large, strong, calm, caring, and confident.
eventually you will use this contrast to gain complete control over him.

1. subtle mental prompts

If you can make the beta male feel like he is vulnerable and delicate (i.e. feminine), he will naturally fall in line and follow a strong masculine leader.
this should be your first goal: to show the beta that he is weak and vulnerable on his own; lacking in strength and manliness - a boy among men. small and cute, and nothing more.
simultaneously you must demonstrate that you are not only strong and masculine, but willing and able to help this beta male by keeping him safe and comfortable in return for his obedience.
That may all sound very intense and complicated, but there very simple cues you can exploit in order to get the desired result:
if you are physically bigger than him, stand close to him and tower over him as often as possible, especially when speaking. Make the size difference impossible to ignore. make sure that he must always look up in order to make eye contact with you. encourage him to sit down whenever possible, so his line of sight is even lower.
use affectionate but condescending body language (e.g. caress his head like a puppy. give him a pat on the butt whenever possible. when next to him, casually put your arm around his shoulders like you would if you were on a date with a girl. horse around - give him a playful shove, pick him up off the ground just for fun. If you want to lead him somewhere, take him by the arm like you would do with a c***d.) These small gestures build up over time, and quickly form an unspoken power dynamic.
if possible, give him small tasks to do for you e.g. fetch me a drink, hang up my coat, etc. whenever he completes a task, praise him so he associates serving you with validation.
give him only feminine compliments: cute, pretty, slender, petite, nice body, nice butt, big lips, pretty eyes, etc.
don't seek his approval or validation. You must be totally self-assured so that he can have zero impact on your social value. your confidence will also make him more likely to see you as a leader.

2. emasculation

demonstrate that he is physically weaker than you
arm wrestle, play-fight, lift-and-carry, etc.
if possible, demonstrate that his genitalia are small, and point out the femininity of his body. do your best to make him feel physically inadequate to ever be an alpha.
if possible, get him naked and confis**te his clothes. he will feel very vulnerable and insecure, and will be much less likely to argue with you. Also, having him naked while you are still clothed creates a very obvious power difference which he will internalize. you want him to get comfortable with you having more power than him.
you must do all this while still appearing as a benevolent, friendly presence. this is the fine balancing act.
you can pass any belittling off as friendly ribbing, or as helpful truth-telling.
the more you succeed in reducing his self esteem as a male, the more you must also reaffirm that he is safe and valued because you are there to look after him.
its important that while you wittle down his sense of power and autonomy, you replace it with a sense that he is valued for his cuteness, loyalty, and obedience.
Emphasize that he is physically attractive, not as a man, but as a femboi/trap/sissy.
reassure him that while he may not be desired by most women, he is very desirable to dominant men.
if you do all this successfully, he will start to associate safety and comfort with being submissive to you.