While some colocation is fairly static and remains the same year after year, most colocation involves careful planning of future growth.  There are a lot of things to consider when planning this growth.  Here are some things to think through.
1)  Realistic Growth Speed. I can’t count how many startups come to us asking about a full cabinet for their 1u server “so we have room to grow.”  Believe it or not, sometimes they fill in the cabinet, sometimes they go bankrupt.  The important point here is that it’s very easy to overbuy colocation so that you can grow into it.  Sure, colocating 42 devices is cheaper per device than 5 devices are per device.  But is it cheaper to have a little bit of downtime later on (to move your equipment) or is it cheaper to swallow the larger monthly recurring cost to allow yourself room.  There isn’t a right answer for everyone, but there is a right answer for you.
2) Know when to rent. Keep in mind that if you have to ship servers to and from the datacenter regularly, it may make more sense to rent them in the first place.  Shipping adds up and it’s just money out the window.  Sometimes customers try to get the most out of 1u by slowly upgrading it from a low end server to a medium server, to a high end server, all the while the shipping costs are adding up.  Maybe it makes sense for you, but don’t forget to factor that in.
3) Give yourself time. A huge mistake we see nearly every day (seriously!) with colocation is waiting until the last minute to pull the trigger on upgrades.  Not all upgrades are instant. Seriously.  If you need a cross connect, it can take up to two months for all of the necessary parties (telcos are notorious for slow times like this) to pass off all the paperwork and complete all the labor.  Plan well ahead for major upgrades and at least know the lead times.  Sorry, we simply can’t deploy 100 cabinets overnight.
Those three tips should set you well on your way.  Mistakes in planning colocation can be very costly, so definitely plan the project ahead of time.