This is really good advice given by vapros and Steve. I just want to add a couple things that bear mentioning.
Vapros mentions practicing going to the end rail and back to your opponent's pocket. It's good to try this with a ball in all sorts of positions: in the pocket, a ball's distance out of the pocket, and with other balls providing obstruction or assistance for the shot. Always have a specific goal for the shot, and consider what speed you need to use to achieve that goal. Practice speeds you'll use to pocket a hanging or close ball, remove a ball, or take a foul.
Also, when playing to survive in the first inning against a good break, sometimes you'll end up leaving your opponent a move in which you'll end up in a worse spot than before, i.e. frozen to the side of the stack or behind another ball or cluster on your side. Practice kicking two and three rails to make a legal hit or take a foul, like these two situations:
START(
%AP2V6%BM3R4%CJ5O4%DM0N2%EM7P1%FI9R5%GK6N8%HN3N8%IK9Q3%JK6M5
%KG4S3%LJ5N2%MK3T7%NF5Z0%OI4M1%PL7L6%WI5D5%XL6L4%YC7U7%ZH9C8
%[D6X7%\C2V7
)END
START(
%AQ2R9%BL7T0%CI7O6%DK6M6%EQ9O8%FK5P7%GK6N8%HM7N8%IM6O9%JE1J7
%KF8S2%LI9M7%MH4U7%ND3W1%OC6I8%PC7H3%W]6C8%XC7H1%Yr1H9%Z^4C8
%[J4[2%\r4J3%]D2X5%^I3[1%eB8a1
)END
In the first shot, you do run the risk of ending up in a bad spot by leaving your opponent some options. You would need to exercise good speed control to leave your opponent frozen or very near to the ball closest to his pocket.
In the second shot, you are in a very good spot as soon as you get behind those balls. Having great speed control isn't as important, although you want to make sure you don't over- or under-hit it.
I hope this has been a helpful supplement to the info already supplied.