Hello there! For low poly modeling I use manly the following training sites:
- cg.tutsplus.com (do a search with low poly and you find a lot of free tutorials)
- www.digitaltutors.com (lots of content with paid subscription, but there are some free courses)
- area.autodesk.com/tutorials (lots of free tutorials for Autodesk products)
- www.design3.com (it has several tutorials for free)
- cgcookie.com (it has several tutorials for free too)
You might need to make a subscription for some of this sites, but all of them offer free courses about diverse 3D software.