To me coaching is one of the most important tasks of an IT architect. Besides guarding quality and long term policies. There are many ways to coach colleagues. And it is an acquired skill, you have to learn the right techniques and communication skills. There are many ways in which you are able to coach. I prefer two of them, but first I'll give you some context for coaching.
Time and place
There's a time and a place for coaching. If you're familiar with the situational leadership model, coaching happens in S2 and mostly in S3. The process in this model is per different task, so a colleague can be in different stages for different task (for example programming) at a moment. In S1 you'll be teaching someone what to do, step by step. In S2 this person is learning different ways to do this task. In S3 someone really knows how to do this task, but may run in to problems and in S4 this person is able to do the task and is able to cope with potential problems. S3 is really the place for coaching. A person does know how to do it an has the knowledge how to overcome a problem, but needs to learn to get to this knowledge. This is where the basic attitudes of the coach (you!) come in.
There are some basic attitudes a coach should have to be able to coach. It's like a foundation on which the coaching relationship is build on. Here are a few:
Coaching is mostly about asking the right questions, most of the time the dumbest questions seem to have the most effect.
Two possible ways
The first way in which I coach i quite subtle. If a colleague asks me a question the easiest way is to give my answer. The coaching way is to ask questions about this question. For example: What solutions have you thought of? The person who asked the question probably knows the right answer!
The other way is by entering in a long term coaching relationship. Agree to sit down once a week or one in every two weeks, try to find the specific coaching question you want to work on and work on it. This is still a goal specific way, you have to set goals and keep on track of these goals, but this process is probably going to take more time.