Editing an imported 3D character which was made with photo shoots I've received a .obj file which contains a model of a real person along with textures which was made with photo shoot as far as i know. I'm completely new with modeling those kind of objects. The object itself is a 800k tri whole human body, which looks really rough, bumpy etc, which i guess is the consequence of the photo shoot. It looks quite good when rendered tho, considering how it was made. I managed to reduce tris to 40k in MeshLab with model looking decent enough but I have little or no idea how to proceed from here. I'm supposed to eventually animate it to walk few steps and sit. But before i do the animation i would like to ask you guys/gals for some advice or tips in the following:

-if any of you had any experience in this kind of modeling, how did you "polish" out the model itself, make it more realistic like it should look in the end, i have some general ideas but i imagine it would take a whole lotta time.

-will joint defining be a big problem in this kind of object(regarding realistic animation), and if so, i'd appreciate some tips on how to animate these kind of object.

I apologize if this is a trivial question, i'm just really hooked into modelling and i'm still deep in the learning process. Thank You very much in advance!
It sounds like you have a 3d scan. Most likely the model will be completely unsuitable for animation in its current form.

You need to create a lower res model with topology suitable for animation using retopology. The basic idea of this is you create a new, simpler mesh, that follows the overall shape of the original mesh (usually using either the shrinkwrap modifier or the snap to surface function in edit mode).

The full details of this are too complicated for a single answer here but there are plenty of tutorials around on the net. I'm hesitant to recommend any because I haven't watched any of them myself. There is a paid CGCookie one, which will probably be decent, but I'm sure there is plenty of good free stuff on youtube.

Once this is done, you can bake normals/displacements/textures from your original model to the new model. http://www.blenderdiplom.com/en/tutorials/all-tutorials/585-normal-baking-using-the-blender-internal-renderer.html looks like a good starting point here.