BMW Cars Programming Advices

I would like to ask what is the safest way to error free bmw programming. They say you shouldn't run the cables thru the window but don't leaving the door open shut off something? It would be great to hear from experience people who program BMW all the time. I also would like to know if they are using a clone icom or real one and if it's VMware or Native install to judge the success and failure rate of both. I think it could answer alot of questions people have.

Thanks