You are bound to make mistakes on your first helmet in what shape to what size you purchase. Unfortunately they are not returnable like mens underwear.
So first of all try to find the correct shape. Then work around size. There will be pressure when first putting on a helmet & in all cases the first week or two will make the difference as the inside of the helmet forms to YOUR head shape unless the wrong shape & if UNFORTUNATELY you choose one that is to small or to large. They all come in clear visors so do not pay extra for a mirror like one or such because the life of the latter is not to good PLUS you will have trouble in keeping the other one SCRATCH FREE.
Do not aim for the top line helmets. For the first one will tell you what errors you made & come a year or two down the road you can upgrade to a better helmet if & when you so wish. The others should be with the DOT or Snell mark on them & such a full face helmet is going to give you good protection.
Now that you have said helmet try to not throw it around, bounce it off the floor or such. Also keep the visor free of bugs & scratches. These to can be done with any form of Plastic Protectant like Plexus, 303, Armor-All, others plus inexpensive Pledge in any grocery store at a low price. The trick in obtain some clean Automotive Buffering cloths at many shops. These are a darn good soft cotton cloth. I carry one in my tank bag along with pledge & one at home. Nothing else is used to clean the visor & when the cloth is around a week old then wash it like by hand or in your washing machine. Do that to your visor & if you are using Pledge then apply it all over the shell to give it a clan waxed finish. Good example is I was into the insurance firm & the clerk noticed my 5 yrs old helmet & said "Lovely new crash helmet" not realizing the age of mine.
Do NOT use normal paper cleaners on the plastic for they really do scuff of the softer plastic compared to clean soft cotten cloths. Lastly my 5 yrs old hemet (a Shoei) is with the visor of a 7 year old helmet which shows how long they can star scratch free IF you take care of them. In my case I can only see with my right eye so if I hit bugs on a hwy run & the right side is a mess then I MUST stop, pull out the Pledge & soft cloth to clean off the mess so I can see properly. I would say on an average I clean my visor 2 or 5 times in a 4 to 7 hr ride plus the time I am home.