I would suggest going back to basics. When I first start adding distractions to Mud's new tricks, I take her to a different area than we normally train(a nearby field) with little distraction. That field is actually less distracting than where I usually train her, but since it's a new place, it is in itself a distraction. If she's not paying attention very well, we play. We run around or play fetch or anything. Mud's one of those dogs that listens better when she's excited because she focuses her attention on me. Then, if she's still not getting it, I do the same things I did when I first started teaching the trick. Then I invited a friend and his dog over, and did the same. Then they came over and a stray happened to tag along. Then I took her to a small park right by a railroad track with moderate traffic.
For instance, on Mud's spins, I of course had only taught her to do one at a time. To get multiple spins, I went back to luring her around, slowly, and just asked for more than one spin. After she was doing this with ease, I gave her the cue twice, and she spun twice. Now she's doing three spins, quickly and smoothly. Don't expect her to get everything in succession immediately. Just imagine for a little while that she doesn't know the tricks. Go back to basics, but do the tricks in succession. First just two tricks, then three, and so on. Even though she does well at home, just go back to "re-teaching" her the tricks as if she didn't know them. She should recognize the luring movements and pick up quickly.
With Mud, for an easier example, I didn't just ask for sit and down in succession quickly. I lured her into a sit, then down, then sit, then down, slowly asking for each quicker until she understood what I wanted of her. Not sure that I've explained this very well. o-0 You also try the "look at me" lesson here on DTA--I use the command "pay attention." You can also use "focus," "concentrate," etc. Anything you want really. You can use this to get her attention on you so that you can train. You said she loses focus after three or four tricks. Okay, so let's say you're asking for spin, back up, sit up(beg), and gets distracted when you ask for a figure-eight. Just go straight to luring her through the figure-eight. Eventually she'll be able to keep her focus for longer.
For the record, I agree with CollieMan. If your dog is completely ready for a competition, your first will be much less stressful for the both of you. I know you're tempted to just dive right in, but make sure you're both ready for it. I don't feel like I've explained this very well, so if I left any blank areas feel free to send me a message. =)
