Although looking at Taylormade will give some examples of the techniques they use you have one advantage:
Your model / actor is already busty!
If your intent is to show the process of BE you have another advantage because of having a busty actor, your can focus your attentions on reactions and props and less on making progressively larger realistic looking boobs.
Here are Kithara's and Nimrod's suggestions for BE when already busty -
1) Spend time on the reasons, story, process or whatever as a good back story will set the mood you are looking for. Even if it is just jump in and grow give it some manner of setting or frame to the story so you have a start, middle and end...
2) Spend time on reactions, feelings, effects and such - it is not just about the boobs. It is not just about going from one size to another - think about the reasons, the rate, etc. There are thousands of flavors of BE.
3) Spend time on the secondary consequences of being more, or suddenly, or randomly busty... Are there embarrassments, jealous friend/enemy, advantages or disadvantages or simply what to do to stand up.
Because you have a busty actor -
Try buying the same shirt in progressively smaller sizes so you do not have to put them in bizarre flexing too get a simple effect.
If you are going to rip clothing - pre-cut or otherwise prep the clothing. You try ripping out of clothing, it is tough stuff.
Use simple tricks of perspective, lighting, vantage point, lens focal length changes, etc.
There are many references in movies, TV, etc. showing BE - think about ones that do it well and how it was done. Many times it is surprisingly simple without using big fake boobs, special effects or having the actor "arch their back".
Movie Examples NOT using special effects:
Death Becomes Her = Meryl Streep 34-B gets a bust boost through magic and it is accomplished "in-camera" by switching her dress and having a staff member literally push her breasts up from underneath. No special effects.
Dangerous Liaisons = Uma Thurman 36-C portrays a younger version of herself and an older and then pregnant version of herself by just strapping her down (then not) and creative costuming.
Evil Toons = Monique Gabrielle 34-D downplays her figure until the evil forces of the film start to take hold and affect the women in the film. It is all accomplished through acting, wardrobe, lighting and suggestion.
She's Having a Baby = Elizabeth McGovern 34-C being the titular pregnant woman deals with her burgeoning bosom in one quick cut scene by simply using a series of smaller and smaller bras. (in later years McGovern got a reduction, why?)