Usually when I start sketching a new part file I take a semi-unintelligent approach and I just through together the rough shape of the geometry first before I put any dimensions on it. In recent years with the advent of the Dynamic Input and Dimensioning, I really should be doing dimensions and geometry at the same time, but old habits are hard to break. I originally learned to build a simple geometric reference and then control the sizing with dimensions placed afterwards.
Now when I did this in the past if I wasn't careful about how much magnitude I gave a certain sketch object, my model would end up being blow out of proportion by my first dimensional change to the model. Even that can be adjusted a little better in recent years with the ability to define default View Limits in a template file.
But now...now I get to be extra lazy with an enhancement in Inventor 2013. Now I can sketch something and even if my overall scaling is way off, when I put my first dimension in, it will automatically scale the entire sketch based on that first dimension. Notice below how it changes the entire geometry based on the change made from the .125 to the .5 dimension value.
One thing to remember about this is that you cannot have more than one dimension on the sketch for this to work. If you have two dimensions placed, simply delete one of them and then this trick will work with a change to the remaining dimension. Compare that to the way 2012 works below if you have never seen this quirk, but I am sure most of you have.