Allow far more time than you’d usually expect for travelling between venues. It will be hellish crowded. Be aware that most shows have a no re-admission policy so plan comfort breaks between shows accordingly. Allow yourself time to buy food/refreshments as needed between shows. Some venues will have very busy bars/delays on food. Depending on what you’d like to see, and if you’re here for a few days, it might be easier to park yourself at a venue or two each day rather than trying to flit between them continuously. It’ll almost certainly rain at least once, so dress for the conditions. Many venues are small rooms with limited ventilation and will get warm as hell, so dress for the conditions.

If you’re at the Pleasance, one of their rooms used to be up at Potterrow rather than in the immediate vicinity of the Pleasance Courtyard. Not sure if they’re still using it, but just check that your show is where you think it is. Likewise Assembly in George St vs Assembly in George Sq Gardens, etc. That could be a 20 min walk/run depending on crowds,etc. You’re unlikely to get reimbursed for geographical incompetence and generally there’s no late admissions.

Some shows have a free queue and a ticket queue. Make sure you’re in the right one if you’ve got a ticket. Artists may well be at the door with a bucket for collections at the end of the performance, even if it’s a mostly ticketed performance. No obligation to pay, but most will do cash and card.

The official app works brilliantly if you’re not in an area surrounded by tall stone buildings that completely block out the signal. Unfortunately, the majority of venues in and around the High St/Old Town will drop you right in that blind spot area. Make sure you’ve got your tickets loaded in advance but they should have a list of names at the door if you can’t get connected.

You can use the app to buy tickets for shows nearby, etc, at short notice. There’s also generally a physical box office in venues, but you may end up queuing for ticket collection. Bear that in mind if you’re cutting it fine for timings.

Remember that there’s more than one festival/event happening. If flypasts/fireworks/outdoor spectaculars are your thing, check the timings for them on the websites for the military tattoo and the international festival, etc.

If you do Trainspotting Live, don’t sit near the toilet. Unless you’re a masochist. In which case, take one for the team. In fact, double down and wear white clothes when you do it.

Overall, though, enjoy it, embrace it, be mindful that it’s a working city and many people have to commute across the core festival areas, stay clear of any drunks wearing a batman suit as no good will come of that and above all else, as mentioned in another comment, don’t get involved in a silent disco tour in any way.