"They all joined together constantly in prayer, along with the women and Mary the mother of Jesus, and with his brothers." - Acts 1:14
The first phrase I learned as a Scout was "Be Prepared". According to the Scout handbook, the idea is: "Be prepared for life - to live happily and without regret, knowing that you have done your best." Big moments in life come without warning and it's too late to prepare. So, the best plan of action is to always "Be Prepared".
One of those big moments was coming for the disciples. They had been through so much over the previous months, but they still needed to get ready. They were instructed to wait for power from on high and they did just that. But, how did they wait? They joined together constantly in prayer. What were they praying for and why did they pray constantly? Above all other considerations, they joined together in prayer to "Be Prepared".