When dining out, I always try to find the new or just-opened restaurants. That is when you are going to typically have your best dining experiences. This is because the newly opened restaurant is trying to create buzz and attract a customer base and also the owners and employees are typically motivated and at their best.
Once a restaurant is established and they have a steady stream of traffic, now they need to switch their focus to profitability. So you start noticing short cuts here and there. The portions are a bit smaller. The drinks are poured more judiciously. Maybe the carpets are only getting professionally cleaned every other week instead of twice a week. Help wanted signs are on the front as some of the original employees start to turn over.
This is especially true with chains, as corporate begins to squeeze for more profit. Some of the individually owned (non-chain) restaurants can keep a high level of service for years and years, but it's tough to do. Most restaurant fail within the first year or two.
My rule of thumb is simple: with the exception of high quality restaurants, I never eat anywhere that I cannot see the food preparation area. And if I see anything I don’t like, I leave and don’t come back. I used to make an exception for new fast food restaurants (like an Arby’s which opened near where I used to live), but they go downhill so fast it just isn’t worth it.
There was a successful restaurateur in NYC many years ago who operated a variety of shops successfully. BUT he had a 6 month make-it-or-break-it rule. If they weren’t successful within that 6 months he’d shut it down. And go on to his next restaurant.