4. Duration. Keep your delivery timeframes short and realistic. It is easier to be successful if your deadlines are shorter rather than longer. Split large projects into "mini-projects" if possible. Keep each mini-project to less than six months if possible. This keeps everyone motivated and focused.'Short' and 'realistic' are not always on the same planet. Delivery periods, rather than being 'short' by some arbitrary measure, need to be set in terms of the risks to delivery that they must deal with, the performance of similar projects in similar circumstances (using 'reference class' forecasting, also see) and with the sponsor agreeing to a probability target for delivery.
This might mean that the sponsor wants to know with, say, 85% probability that the deliverable will arrive by a certain date.
Your durations will need to include various buffers, an idea developed in the 'critical chain' literature, but generally applicable.
Durations also need to have an eye to performance or capability delivered and configuration issues that might attend the options or trade-offs for any capability-timing 'couples' that exist in the project.