Congrats on the training gig Anton! I started in a similar situation. I had been working at a gym for awhile and they knew I wanted to start training people. I got certified and they said "Great, teach this class once a week". No guidelines, no information, just here's a list of people whose money we already took and you're supposed to get them 'in shape'. The obvious upside is no oversight but now I had to actually do it. Very nervous like you described, a few sleepless nights. Here's roughly how I approached it with my admitted lack of experience:
1) Warmup. Joint mobility drills, agility ladder if you have one, read Robb Wolf's 'Kyphosis' article in the PM. Great warmup routine there.
2)Evaluate first. Instruct form/technique on the basics like: Pushup/Pullups - can they do any? How many? If not, plank holds, pushups on wall or box working towards horizontal, ring hang-for-time, inverted bodyrows on rings. Situp test, do they/you have an abmat? Very portable and can do 'supermans' or back extensions with it too. Air-Squats - Instruct form, go over CF squat article(s) videos, Rippetoe's squat teaching progression - all great info for coaching. If time allows, formulate and run them through a circuit using these basic exercises.
3) You said they do have dumbells. Go to Coach Rut's blog www.coachrut.blogspot.com
. He posts daily workouts, lots of dumbell workout ideas. Don't forget BrandX Martial Arts site for scaled down WODs depending on the level of your athletes there. Speaking of levels, use Dave Werner's Skill Level Assessments. He generously posts them on his site at www.crossfitseattle.com
. They are great for giving your athletes a perspective on where their fitness stands.
Sorry for going on and on. There is a ton more I know I forgot or should be doing myself. Have fun with it. If you really want to coach then you will have a blast overall just figuring it out and it gets more comfortable every time you do it.
All the best,