-Plan, but not TOO much. Know what parks to do on which days, have a list of must-dos for everyone in the group, and have an idea of where you would want to eat for each meal, so come busy lunch time you aren't waiting in huge lines, hungry and frustrated
-Don't do TS locations everyday. Pick 1 or 2 TS locations that sound as if they would fit your tastes and space out what days you do them. Choose ones that are in the parks you are planning on spending the day in or at your resort, so that you aren't confusing yourself with transportation.
-Comfortable shoes!
-Bags can go on the rides with you as long as they are small enough to fit in the pouch on the ride vehicle. (I usually don't bring anything bigger than 12"x12".)
-Use the bag to bring water in with you in the parks! And snacks! Don't bring too much though or your shoulders will kill. I use a Bobble or Brita water bottle so I can just share 1 water bottle between my boyfriend and I and it's less weight to carry. That way we can just fill it up on the way to an attraction and drink in line!
-Plan for at LEAST 5-6 days in the parks if they are doing only the 4 parks! Plan more if they are doing water parks or Universal etc.
-I PERSONALLY would say no park hopper for a first timer. It might be overwhelming.
-I would tell them about photo pass, ADRs, EMH, Transportation, and fastpasses! How to explain them simply?
-Photopass- they give you a card. You walk around the park and see CMs with cameras taking pictures of people. Wait behind them and hand them the card. They will tell you where to stand, what to do, etc. When you get home log in to the website with your photopass card and your pictures are there!
-EMH- A different park is open earlier or later each day for Disney resort guests. Only visit the parks with this option on these days if you are visiting during that extra hour or 2, otherwise it's not worth it since those parks tend to get more crowded.
-Transportation- Even if you are the type of person who prefers renting a car, you might find it worth it to take Disney transportation as a first time visitor. There are buses from each resort to each park and DTD, but not from resort to resort, or park to park. The buses stop running an hour after park closing, but DTD runs late.
-Fastpasses- There are kiosks with "tickets" being dispensed for select attractions. The tickets have a time to return and ride that attraction. Use this if you don't want to wait in line, but you must return within the hour window listed on the ticket. There is also a certain amount of time listed on the ticket specifying when you can get another fastpass for a different attraction (so you can't hoard 8 fastpasses for attractions throughout the parks, you are only allowed 1 at a time, usually)
-ADRs- If you are planning on dining at a TS location, you most likely need to make a ADR. Just go online and browse the website!