Interesting coincidence that you're asking about a Slow Stick, I just hooked up the radio in mine tonight. Some things to check/do:
1) Turn on the transmitter first.
2) Confirm that both the transmitter and flight battery are charged.
3) Are you sure you have all the servos plugged in correctly? If you're using Futaba servos and receiver, this shouldn't be a problem, the alignment tab forces correct polarity, but others may not.
4) Keep the receiver antenna away from other metal. Mine was glitching a bit while it was still coiled up and near the fuse tubing.
5) Confirm that all your electrical connections are tight.
That's all I can think of for now, I'm sure others will have some additions.