KNOW your menu, ingredients, prep/cooking techniques. A lot of folks nowadays ask the wait staff detailed questions about where the ingredients come from, how were they treated (ie: animals), etc. You don't have to know it all, but you are frontline between customers and matire D, wait staff (if they're too busy) and/or chefs so better to be prepared than to give customers a blank stare (or make up some BS) and compromise the reputation of the restaurant.
Remember, diners nowadays can be reading reviews of the restaurants they're eating in in real-time. They may know MORE about your restaurant than you do. So be prepared and informed.
Every restaurant works differently, so they should tell you what is critical in their "machine". That said,
I second knowing table numbers and seat positions. As a runner those should be second nature and you'll get evil looks if you keep bringing food to the wrong tables or people.
Knowing the menu is important too - not because people will ask you about it in general or for recommendations (you will be bringing the food, not helping them decide on what to order) BUT you will be amazed at how many people will ask you "tell me what I'm eating again" when you bring food - especially at nicer restaurants where there are multiple courses and/or longer periods between ordering and service. So you should be able to at least explain the dishes you are bringing.
Don't put your fingers in peoples food
Don't pass over people
if you've never run food and you're carrying plates out on trays - practice - don't rest the tray on your shoulder (though you'll want to) it isn't as stable
If the front server isn't there when you drop the food, ask if they need anything else (another great time to know your seat positions), we always expected the runner to get anything they needed (silverware, napkins, water, etc) except alcohol which the front server should ring in and deliver
When you're in the weeds your primary role is to run food, don't leave hot plates in the window ;)
Make sure that you know who's responsible for having the correct cutlery on the table before you deliver plates. Our chef was incensed any time an order was dropped before the table was "mised". Even if the server was ultimately responsible, it was the food-runner's job to check beforehand.
First, congratulations on the new job!
Second, it's a great sign that you are so enthusiastic you are trying to do some homework or research before you even start, kudos, that's the right attitude.
Third, I would pretty much ignore all of the advice you have been given (not saying that any of it is wrong) but rather use this as knowledge, but don't go into the job thinking something you have read here is "the way it should be done". Frankly most, especially chains, have extensive policy and procedures on what and how they exactly want the job performed.
Congratulations again and best of luck!!
Knowing your menu is essential these days, especially with dietary requirements.
Make sure you know about gluten free, coeliac disease (same thing), dairy free, egg free, nut allergies, vegetarian, vegan, lactose intolerance, pescatarian (vegetarian who eats fish) and the other myriad dietary needs.
Your wait staff should have already covered this but be aware you will be asked "is there gelatine in this pannacotta?" Etc. (there is, and you should perhaps know if it is porcine derived)
Homework is the key.