[Mpatas]

I have difficulties sometimes to visualize complex molecules in a 3-d manner.

Any suggestions what is the best way?

[discodermolide]

Buy a set of molecular models.

[Babcock_Hall]

Models are great, and I recommend them for biochemistry as well as organic chemistry.  However, I also suggest that people practice drawing and rotating molecules on paper.  For cyclohexanes, Newman projections are tricky to draw but are great for seeing 1,3-diaxial and gauche interactions.

[zsinger]

Models are the best and only way to truthfully learn this stuff at an introductory level.  Once you get through Organic 1, much of this will become second nature in your head.  However, start with models!!!!!
            -Z