I have lived in Houston for 4 years and have used three sources for finding the best restaurants:
1. Personal Recommendations
There are a few restaurants that were mentioned over and over again when I had informally surveyed people for restaurants upon moving here. They include local favorites such as Fogo de Chao, Pappas Restaurants (Pappasito, Pappadeux, Pappas Bros., etc) and Lupe Tortilla, to name a few. I found that the quality of the recommendations was even better when I began to specify the type of cuisine I was interested in, which is how I found my favorite, Kata Robata - the best sushi in town!
2. Alison Cook's Top 100 Houston Restaurants
I like Alison Cook's restaurant recommendations. Her Top 100 features a great short summary of the winners and also includes nice pictures. I've tried several of her top choices and agree with her palate. Below is a link to the current list.
Yelp is an invaluable resource when you are new in a city or an unfamiliar part of a city. I have stumbled upon some terrific places based on ratings from Yelp users. I tend to trust ratings that have a lot of reviewers more than those with just a few reviews, and so far haven't gone wrong using this method.
Good luck and enjoy exploring in this foodie town!