As a frontend dev, you are uniquely qualified to find all kinds of holes in a design and problems with flow. When that happens you will have to stop what you are doing and go talk to the designer or even the client to figure things out.
This cycle of code and problem discovery tends to significantly hurt development and the end product.
To maximize your time in front of the screen, here are the three things that you should demand before you start coding.
1. A Wireframe / Flow diagram of the app
This sounds trivial but really is the most critical piece of the entire puzzle. Simply put, every nav element's end point should be defined. Questions like "How do you get from page X to page Y?" should be illustrated and explained. This cuts down app flow confusion on your end along with helping to clarify the product's interaction touch points for everyone involved.
Check out http://www.mockflow.com/ for creating interactive wireframes.
2. A Style Guide
Obviously, things WILL be lost in translation between the design team and your eyeballs as you convert the psd into [insert your flavor of css]. A style guide that gives you set padding blocks, font styles, color hexes, and button styles will make your life so much easier – not only will it help to keep your code dry through the use of extends and mixins, it will also make your implementation more correct on the first iteration.
Check out http://csshat.com/ for designers to give you CSS rules with no pain at all.
Have a defined scope of what you will be doing. Are you supposed to skeleton out the html with dummy data and style it? Or are you supposed to hook up the pages with real data. This information will help you to better divide and conquer the work in the most effective way. It will also give you a better way to determine if something is actually done.
I Hope this helps