5e starting group

>>55069239
Most UA (unearthed arcana, semi-official PDFs put out by wizards as playtest material) is good, particularly the player options. Avoid the Theurge and Lore Wizard wizard archetypes, they both serve to make the most versatile class in 5e, the wizard, even more versatile without sacrificing any power, even compared to the "best" default archetypes.

The PHB ranger is bad, even if not using ANY other UA content, steer ranger players to the US Revised Ranger.

Don't let players try and game for more skill check attempts, nothing breaks DC math harder than letting 4+ players roll that d20. The "help" feature exists for a reason, if multiple people are trying it and the action benefits from numbers, they get advantage.

Advantage and disadvantage are binary and cancelling. Any disadvantage negates any advantage and vice versa, they aren't weighted.

Spells do what they say. This may seem obvious, but i've dealt with a high percentage of former 3.pf players who try and use spells wrong. Grease is slippery, not flammable.

Concentration checks. It's a big part of how casters function in 5e, on both sides of the screen. Make sure players are rolling them every time you deal damage. I suggest some sort of colored or lit denotation of concentration, so you can always see at a glance. I use a similar system, via red/green post-its, to denote reckless attacks on a barbarian in my group.

If a player wants to play a Warlock, make sure they understand that they will be playing, essentially, a martial with caster flavor, not a wizard with beams. Most rounds will be eldritch blast.

Encounter math feels off for new DMs, remember that you are expected to run 6-8 total encounters, more if "easy" less if "deadly", in a long rest period, with 2 short rests mixed in. For many DMs that means upping the encounter rate or lengthening the rest times. If you expect 6-8 encounters in a week, set it up so that a long rest is a day off and usable once per week instead of per 24 hours.