I've had my fair share of learning about the enneagram and participating in quite a few online forums. I couldn't find anything like this on 16types for the enneagram, so I figured I'd chip in a bit of my understanding.
1. It's not a personality theory.
In this context, the enneagram is a psycho-spiritual tool used to better understand your deep, hidden inner fears and defense mechanisms. These can sometimes give us correlations that tell us things about what a person may be like, but there is no determining factor here.
2. Don't type by "motivations"
What motivates you on the surface of things probably has nothing to do with these deep fears, etc. The ones that apply to the 9 types are generally a result of those defense mechanisms, which means that you can't start with just the motivations. In other words, you would have to clearly be aware of your inner workings to effectively understand your motivations; in which case, you would already be aware of your type.
3. Cross reference from the ground up
There are core elements to every type. These elements are usually a good way of checking your understanding of what you're doing. However, descriptions that only reference a common personality should be considered arbitrary and useless.
4. Descriptions are a good aid, but never type based on your impression
Try to think critically about what the description is really saying about you. If you cross apply what you know about your deep, inner workings, then you will probably be much more accurate in your self typing. And yes, I know, 4s are very dramatic; and very much so unlike everybody else, they feel so misunderstood.
5. Remember that your wing only influences your habitual way of coping with these core fears, etc.
So if you're a 3w4, your inner workings aren't necessarily any more "4ish". However, a 3w4 will have a 4ish bent to how (s)he deals with these fears - meaning that (s)he will probably look a lot like a 4w3 on the surface. This applies to 6w5/5w6, 7w6/6w7, etc.
^ Cross apply the above for growth/stress arrows.
See also: this article