Backstop, temperature is as much a key when smoking as is the rubs/smoke/marinades etc. Being able to monitor the temperature of the smoker and the internal temperature of the meat is invaluable. If you don't have a temperature gauge on the smoke chamber of your offset I'd highly reccomend you fit one - you can buy an accurate dial type of ebay for about a tenner. Then also, a temperature probe for the meat, you can pick up a digital read out one with a flexible cable and probe that you stick in the meat and run the cable to the outside of the smoker. With that setup - probably 20 quid for the two, you can produce some excellent smoked food. Once you start looking recipes from our American cousins, who are years ahead of us when it comes to this kind of cooking, you will see that cooking to an internal temperature of the meat will guarantee consistant results rather than cooking for xx hours per pound of meat. It will also allow you to be more economical/practical with your cooking, for example, when the internal temp of your meat on the smoker hits 140F, the smoke ring is set and it won't take on anymore smoke flavour, therefore you can stop throwing chunks of wood in the fire box, or, heaven forfend if it's peeing it down and blowing a gale, you could transfer the meat the the oven.
For a really cracking book on hot smoking and barbeque for rubs/marinades and techniques, try a book called ''Big Bob Gibsons BBQ Book'' by Chris Lilly.
Good luck, I'm sure you'll have plenty of fun experimenting.