There are certain mechanics to the game in GG that you can relate to. I have a friend named Rod who plays GG. The best way I'd explain it is through the similarities first and then the differences.
For one, roman cancelling without a special input (GG mechanic) is drive cancelling here. Go from there and explain that kind of thought process. Some characters in BB have setups after grabs or are used to doing combos into attacks. Take Kensou for example. Off of a grab, he can get a full combo using EX meter. Grabbing, if I remember correctly, is an important part of competitive BB and GG. Teach them about throw invulnerability and when to do it, what they can do from the setups on knockdowns. Although it's not specific to GG or BB, a lot of players I've seen like the thought of setting up safe jump setups that come from that type of game. You can setup safejumps from hard knockdowns and stop safe jumps by recovery rolling soft knockdowns.
Lastly, some moves in GG and BB have properties that allow them to do long combos. I'd say a huge similarity between the two types of games is the use of specials in neutral game and with follow-ups. Although each character has a unique sense of gameplay, almost all characters have some sort of way of following up some attacks (either in the air, off a juggle, a knockdown, a grab, or hitconfirming a special with a follow up). Properties change with EX or counter hit moves that is also very relevant to neutral game and in combos. Sell the mechanics on the similarities.