The Meaning of Life, the Universe, and Everything.
To make a professional map, figure out what you're going for. Do you need space for an arena or spawn that's huge? Do you need a forest cleared? Are you looking for unique landscapes or structures?
I can use my upcoming server as an example. We're a pvp server with factions. I need a good place for our asylum spawn (and shop), arenas, and want lots of mountains and custom trees, treasures, and a volcano. You could use TerrainControl, which allows you to edit text files to control things that are generated in each biome. It is however complicated. I prefer using WorldPaint and WorldEdit right now. Worldpaint allows me to lower, flatter, raise, indent, clear, ect the land in any biome with custom brushes. I can also create custom forests out of schematics or clear out a forest entirely without having to set fire to it all or crash my server world editing it all out. I can smooth everything out too so that it's more natural and less "hey, I just landed here." World edit is going to be amazing for finishing touches, customizations, and building in general. Try to avoid that cut and paste look. Make it look built by hand (making sure everything is turned the right way, for example). When you know what features are interesting or popular, you can get an idea of what you want your world to have. For example, a shop. Some servers sell every item known to man, some are limited. Take some time and see what you like and don't like from other servers. Create a unique experience. If building isn't your forte, get some builders or go hunting for schematics that are free to use (you can even edit them for great effects). If you aren't sure how it looks, beta test and/or get friends to check it out. The shop I recently made disappointed me, but was widely loved by players. Ya just never know Take their feedback and grow with it.
.rars are much worse as not everyone has WinRAR or 7zip and don't intend to get it for whatever reason.
So unless it's pre-installed with the operating system a way to handle a fileformat then it's bad?
You didn't say anything about the compresion levels and effectivenes of .zip vs .rar formats.
A fine subjective statment you make in other words
Anyways this isn't much a tutorial, if you'd want to create a tutorial there would be a lot of information on how to plan for a map and how to acctually create it. All you say here is "Tutorial, how to create a professional adventure map: "2. Create it!"