Regardless of who you choose you should follow these rules.
First make sure they are licensed and insured and ask them to provide documentation you can verify. A reputable contractor will have no problem providing you with copies of these documents.
Next ask for several client references and do not be afraid to call and ask questions like did the contractor complete the construction project on time and within the budget, did it meet your expectations, how neat were they in your home, did the workers show up when expected, etc. If possible ask if you can see the finished home remodeling or renovation work the contractor did.
Call the better business bureau and see if there are any complaints filed against the contractor. Visit http://www.bbb.org for more information
Visit http://www.nari.org to learn more about NARI
Visit http://www.nari-ny.org for Information on the NYC / Long Island Chapter of NARI
Also check online to read long island contractors reviews from customers that have used them. Sites such as Find A Pro and Angies List are excellent resources.
So whether you want to do a kitchen remodel, bathroom remodel, dormer or a build a new home, by doing research and comparing contractors and materials you should be able to find a reputable contractor.