Hi,
well that all depends on what you actually want on your bases? Rocks, water, forest? There are many tutorials online already, check this out:
http://jomada-adventures.blogspot.de/2013/04/tutorial-goblin-town-bases-step-by-step.htmlhttp://jomada-adventures.blogspot.de/2013/03/tutorial-azanulbizar-bases-step-by-step.htmlhttp://massivevoodoo.blogspot.fr/2010/01/tutorial-building-base-with-wood-from.htmlhttp://massivevoodoo.blogspot.fr/2010/01/tutorial-basing-with-cork_06.htmlhttp://massivevoodoo.blogspot.fr/2010/05/tutorial-making-snow-advanced-way.htmlThese are just a few examples, but if you tried out a bit by yourself, you will fast become good at seeing what works and what doesn't. One simple rule: don't overdo it! In the beginning, all these techniques look so cool that you might want to try them all at once, which often looks a bit unrealistic. Also, think a bit about the background of a mini to get an idea which type of scenic base could fit, e.g. goblins-rocks/snow
Also, something which I do very often, is to browse coolminornot and to look for cool bases (especially on gaming miniatures, where the space is limited by the base)-which is great for inspiration