How can I tell if I'm putting my RI on too thick or too thin on my cookies?? I border and then flood, but think I am using too much frosting. Any expert advise is appreciated. I do cakes and fairly new to cookies but love doing them. Thanks

There's no rule here, just preference. What makes you think you are putting too much?

Also, I usually border with a 3 tip and fill in

well, now that they dried I can see the layer. Looks ok I guess. Just seemed like I was using a lot of frosting. Think  it may have been a little thick too. adjusted it again. thanks for your help

If you don't want to outline & flood, just put the icing on with a spatula. or make it thin enough to pour.

i am new to cookie decorating and have seen video tutorials of people outlining and flooding, and they flood with #2 or 3 tip i believe and leave some gaps then use the needle tool or tooth pick to fill them in. that way you can ensure you aren't flooding too much. otherwise if could run off the side. 

http://www.cookiecrazie.com/2012/03/cookiecraziebasics-decorate-with-glaze.html

http://sweetopia.net/2009/09/how-to-decorate-cookies-with-royal-icing-top-10-tips/

http://www.sweetambs.com/tutorial/royal-icing-consistencies/

Now to a glaze icing (not royal icing)

http://www.cookiecrazie.com/2012/02/cookiecraziebasics-glaze-icing-recipe.html

Wether or not you need to pipe an outline depends on what you want you bickie to look like and how runny you make your royal/glace icing.