Dependant on your personal goals and ability I have put different options on reps & set ranges.
Stability - light weight typically 50 - 55% of the maximum weight you can perform only one rep with. (%1RM)
18-20 reps - 30 - 45 second rest between sets
Endurance - medium weight typically around 60 - 65% of the maximum weight you can perform only one rep with. (%1RM)
12 - 15 reps - 60 second second rest between sets
Muscle building - Heavier weight typically around 75 - 80% of the maximum weight you can perform only one rep with. (%1RM)
6 - 8 reps - 2 minute rest between sets.
When performing these exercises it is important to do so in a controlled manner, the lowering of the weight is just as important as the lift phase. Ensure to keep the core tight at all times.
If you do not have physical weights, you could always use tins, bottles of water, filled milk cartons or even bags of potatoes.