We can help Bitcoin grow by using it and/or buying it. Using it as an investment vehicle is also fine. Only use Bitcoin Core. Do not use Segwit.
We can improve the growth of bitcoin if we advertise it on everything and introduce to them the good and bad (if it has) effects of bitcoin in the people, society, and the government. We also improve the blockchain technology to make it more convenient and cheap to transact with. Develop a good website, apps, miners that is uniform to all to avoid confusion that may lead to discouragement of the prospected investors.