You can remap the escape key from ctrl-A to be another key of your choice, so if you do use it for something else, e.g. to go to the beginning of the line in bash, you just need to add a line to your ~/.screenrc file. To make it ^b or ^B use:
escape ^bB
From the command line, use names sessions to keep multiple sessions under control. I use one session per task, each with multiple tabs:
screen -ls lists your current screen sessions
screen -S <name> creates a new screen session called name
screen -r <name> connects to the named screen sessions
When using screen you only need a few commands:
^A c create a new shell
^A [0-9] switch shell
^A k kill the current shell
^A d disconnect from screen
^A ? show the help
An excellent quick reference can be found here. Worth bookmarking.