Conversion to mobi

Hi there! How should I go about converting other file formats (specifically epub, lrf, pdf) into a decent mobi file. I tried using calibre to convert however, the results were not at all to my liking. i recently read one mobi file which had a very good format. It was easy to maneuver around the book and the text was nicely formatted. By maneuvering I mean that it as easy to go from chapter to chapter, table of contents was very well done, etc.

Can anyone give me any advice on this? I'm really new to this.

Thank you very much!