To be able to create 3D models, or train your mind to think in terms of 3D modelling, the process boils down to familiarity;
Be familiar with the capabilities of the software used.
Be familiar with the subject of your creativity.
Be familiar with how modelling the subject can work within the capabilities of the software.
Be familiar with how many ways there are to skin a cat (i.e. more than one way of doing something)
Play with LEGO (a lot)
Play video games and try to work out how the models within the game are made - but ignore the low poly count and visual smoothing.
Download free 3D models and dissect them, see what makes them.
And above all...
Have fun!
Paul