Teamkilling is a result of bad teamplay, nothing more. Yes, you can put your team in danger if you're overly cautious but thats not your mistake, it's fault of everyone included. Good teams have no such problems.
People usually stay next to each other when they are ganking someone and rarely come from behind. Against some builds, that's pretty stupid thing to do (high shield skill, spammy weapon).
Give some space to your allies, form a circle around the enemy and don't stay in his range, slowly advance towards him (the whole team) and watch closely for his reaction. No one can beat team which does it properly, only teams who don't use their head fail against single opponent.