Times Square/The Theatre District is not known for having the best restaurants in New York. Here are a few I would recommend. If you are willing to take the subway or a cab outside of the theatre district, your choices are endless:
Le Bernardin (unequivocally the best high end restaurant in the theatre district)
Carnegie Deli Carmine's Tony's Di Napoli Don Antonio Patzeria Perfect Pizza Patzeria Family & Friends Basso56 La Masseria Toloache Sushi Zen Lamb's Club Aureole
You have gotten some great suggestions here. But keep in mind that the theater district gets very crowded before a show. Plus, construction seems to be everywhere (narrowing the sidewalks). Even walking three blocks up or down Eighth Avenue can be very stressful. It's nuts.
For that reason, whenever I eat before a show, I like to stay as close as possible to the theater. That means, for me personally, on the same block! Then, assuming you already have your tickets, you can use the facilities in your restaurant and then stroll over to the theater about 10 minutes before the show. No stress! This makes theatergoing a pleasure.
Anyway, before I saw Cabaret, I met some friends at 54 Below and sat at the bar for a cocktail and a delicious salad. This location is great because you will be in the same building as the theater (or close enough). Call ahead, though, to make sure a show isn't going on and that sitting at the bar is possible.
I didn't eat before Gentleman's Guide, but for that I would recommend Pigalle, on the corner of Eighth and 48th.
I completely agree with macnyc's suggestions. On evenings when you are going to see a show, stay as close to the theatre for dinner as possible due to winter weather, construction, and crowds. That is great advice. It will save you a lot of stress.
And if you are around on another day without an evening show to get to, pick a place to dine somewhere else in the city. I love Buddakan, Bouley, Scalini Fedeli, and Del Posto outside of the theatre district.
Just make reservations. Theatre district restaurants are mobbed before and after the show and December the absolute busiest time of year anywhere in the city. I'd rather leave in December than in July/August!
Also around the corner from Gentleman's Guide is Trattoria Trecolori, which has been very good at previous visits. But I tend to disagree with macnyc about limiting yourself to the same block; as long as you're within a few blocks of the theater you can walk within minutes. Lots of good choices!
La Masseria is the best Italian restaurant in the Theater District, and it happens to me just a few doors down from The Kerr, where Gentleman's Guide is playing. I highly recommend it. Make reservations, though--it's always full-to-bursting pre-theater. La Masseria website
I highly recommend Trattoria Trecolori, at 254 W 47th. Very reasonable prices for the area, and very good food. As others have said, make a reservation.
"It does me no injury for my neighbour to say there are 20 gods or no god. It neither picks my pocket, nor breaks my leg."
-- Thomas Jefferson
Yes, by all means make reservations! OpenTable is a very good app for that. It's free. Just sign up, choose a restaurant (you can search by name or by location) and pick a time. Very easy!
If you don't have a smartphone you can use the website, opentable.com. Or use both!
Also near Gentleman's Guide is Mont Blanc (Formerly Luxia). Sit at the bar for cheap drinks and some good European food. Not touristy at all, and has a great old NY vibe.
"If this is going to be a Christian nation that doesn't help the poor, either we have to pretend that Jesus was just as selfish as we are, or we've got to acknowledge that He commanded us to love the poor and serve the needy without condition and then admit that we just don't want to do it." -Stephen Colbert
I also would recommend LaMasseria and Trattoria Trecolori....have always had good experiences at both of these restaurants. I also agree that a reservation is a must.
Once each trip I do restaurant row Pre-theatre at Don't Tell Mama and post theatre at Joe Allen. It just feels 'theatre'. If you make a post theatre reservatikn at Joe Allen just tell them what show and they'll book you for the correct time.
Love Becco,Orso, Barbetta
Also Havana Cental for Cuban on 45th. All take reservations and will get you out in time for curtain. Just tell them-it's what they do.
I hate eating near the Theater District, and as a rule, I make every effort to avoid it (including the entirely undeserving-of-three-Michelin-stars, Le Bernardin. That said, I adore Ippudo and will suffer crowds and lines for their ramen. Betony and Seäsonal, just north of the theater district, are also amazing.