A good way to learn to code private servers it to learn to code...
That's really all there is to it. Chose a programming language that you want to work on private servers on and then take a step back and LEARN THE LANGUAGE before you even attempt to do much with a server.
Keep in mind C++ is incredibly powerful but can be more time consuming to develop a full project and for many people is more difficult. C# is what most pservers on this site use and it's a very workable language (plus you'd have loads of examples from other sources). Java is something that works quite well also but not really any examples on here (Qonquer was written in java). There are TONS of other languages you could use but generally you want one of those 3 for this type of a thing.
There are a bunch of programming guides on here and the internet in general. I'd suggest reading through infamous' programming guides in the programming section (stickied so easy enough to find). I've been posting this link a lot lately but heres the full e-book for C# for dummies. It contains a ton of good basic information to get started.
<edit>
Just warning you now... if you aren't willing to spend a significant amount of time LEARNING (I mean reading, trying things, asking (intelligent) questions and basically getting frustrated from time to time) then I suggest you stay out of programming... if you want to go anywhere with it you'll need to put a bunch of time into LEARNING. IE: weeks/months.