Best way to use most BA and infantry is to think of them like semi-mobile minefields. Drop them off in some nice terrain(pretty much anything that isn't right in the open) that you don't want your opponent moving into. They can relocate a bit, but overall their job is to stay in that general area and make hostiles regret entering that particular patch of planet.
And if nobody goes near them and they never end up firing a shot, that means that decent-sized patch of map was owned by you the whole game. Win-win.
Unless you have a fast means of moving them across the map (such as a fast Omni, APC, or air transport), they work best in games with objectives where one side can play the defender. Place them where your opponent HAS to go, and they have no choice but to poke the hornets nest.
If you do have fast transports, you can use them offensively. That group of assaults and heavies sniping across the map from heavy woods cover? Drop some squads on top of or right behind them, and I can promise they won't be staying in those woods for long.
![evil :evil:](https://bg.battletech.com/forums/Smileys/default/evil.gif)
Finally, don't forget that BA can use Infernoes, because there's a good chance your opponent will, and a single Inferno-10 salvo is a fun tool to keep in your back pocket.
![Cool :cool:](https://bg.battletech.com/forums/Smileys/default/cool.gif)