Order of ingredients when making Pizza dough
I read two or three different questions here:


Should I dissolve yeast in water?
a. Should I proof yeast?
Should I mix wet ingredients into dry, or dry into wet?


1) You don't need to dissolve active dry yeast in lukewarm water anymore (if you're using some other kind of yeast, this may not apply).


  You may have heard over the past year or so that active dry yeast (ADY) has been reformulated into a smaller particle size, and can now be used without dissolving it first – as had always been the requirement....
  
  You don't need to dissolve active dry yeast in lukewarm water before using it. (Even though it still says you should dissolve it on the back of the yeast packet, if you buy your yeast in packets.) 


"Active Dry Yeast: Do you really need to dissolve it first?" King Arthur Flour

1a) Proofing yeast doesn't improve anything in the dough, it's just a means for you to discover whether your yeast is still active. If you bought it relatively recently, from a relatively busy story, you probably don't need to worry.  

Yeast packages often have expiration dates.  I've found them to be not all that accurate.

2) Typically we add wet to dry: Order of combining wet and dry ingredients when baking

The gist is, dry powdery substances tend to float on top of water and form a skin.  Adding the water to the flour (better) prevents this and tends to allow the wet ingredients to be incorporated more easily.

So, putting that together, you should mix the flour, salt and yeast (unless you think you need to proof it), then mix in the water (and oil, if you're using it).