You might have the best knowledge of technique in the world, an excellent eye for details and an encyclopaedic memory of every man to play Test cricket for your country, but none of this will automatically make you a good coach. Of course, you need an understanding of, and love for, the game - but, for me, the most crucial aspect of coaching is the ability to pass this understanding on to the players that you coach.
To do this, you have - and this is essential - to be respected by the players. This doesn't mean that they need to see you as someone superior to them (look at the most successful coaches and managers in both cricket and football), but as someone who is worth listening to and they like working with. Every player - especially at junior levels - is different, and there's no catch-all approach that can be used to build this relationship. As a general rule, however, showing the players the respect that you'd like them to show you isn't a bad first step. No matter how old they may be, there shouldn't be any reason to treat them with any differing levels of respect.
This doesn't mean using the same technical language to an 11-year-old who has just put on a pair of wicket-keeping gloves for the first time in his life as you would to a 19-year-old who regularly keeps wicket for the club's second team, but it does mean to explain and reason what you're telling them, rather than just giving out orders. You wouldn't take kindly to someone telling you that something you're doing is completely wrong, and then being told to do it entirely differently without any justification. This 'method' doesn't pass across any understanding of the game, and should the player develop any problems later, he won't have a foundation to base his thoughts on.
Technical jargon isn't necessary to convey an understanding of any of the aspects of cricket. Any shot a batsman plays - and, to a similar extent, wicket keeping - can be related to the need to be balanced as shots are played or the ball is taken. Bowlers don't need to hear the word bio-mechanics unless they have a highly unusual love for physics - it can all be expressed in terms of keeping everything co-ordinated in the same direction, and smoothly. Teacher training courses talk of 'scaffolding' knowledge - applying things that players already know (either in the field of cricket or elsewhere), and building on and around these.
Take the 11-year-old wicketkeeper, for instance - if he's a football player, then it's easy to relate the basics of keeping to being a goalkeeper. A link such as this will often save you from spending time conveying topics such as the stance and being balanced and alert in a more abstract manner. It's often effective to ask a batsman why he's doing something, or ask him to describe what he's thinking when he plays a shot and then challenge these statements rather than coming in straight away and pointing out errors. This process of debate, which the coach should always 'win' as the player understands the flaw in his technique, has the vital side-effect of passing on the understanding of the area to the player at the same time.
Of course, the above method won't work for all players - some need to have the flaw exposed more obviously (unfortunately, this often happens in matches), and others will start thinking too much about what they're doing rather than just doing it and shatter their own confidence through the following downturn in performance. As has been said, it's far easier to make a player worse than make one better, and in the case where a player starts to struggle in this manner, the coach should try to put all ideas of technique and analysis to one side and reverse the cause of the problem by shifting the emphasis back onto effort and enjoyment rather than thought! A sense of humour, whilst always useful to lighten the mood, is at its most essential in these instances where the best course of action is often to empathise with the players, and through this improve both their mood and confidence. One smile can go a long, long way.
As the coach/player relationships develop, these instances will become fewer and fewer as the coach learns what exactly to say, and when to say it, and the player is able to actively assess what he's told. There often comes a significant point where the coach notices the relationship has changed from the early stages towards an understanding - this can come after minutes, weeks or even months depending on the personalities of player and coach involved, and can transpire in many ways; the player asking the coach something through his own volition, or critically commenting upon a coach's suggestion are two of the most common 'markers'.