First level HP are just too low right now. I recommend that they be increased to Constitution score + hit die. Right now, it's just too easy for a first level character to be one-shot. I realize that 1st level characters aren't exactly epic heroes, but this is ridiculous. For example, 1st level combat spells do more than enough damage to outright kill a 1st level character with ease. Magic Missile does 3d4+6 (avg. 13.5) damage and always hits. Inflict wounds deals 4d8 (avg. 18) damage. Burning Hands and Thunderwave deal 3d8 (avg. 13.5) damage to an area.
A first level fighter has at most 10-15 hit points. Any of these spells could kill him in a single hit. It's even worse for other classes with smaller hit dice. Even with the change I am suggesting, these spells would still be quite deadly, but not ridiculously so. And it's not just spells. Weapon attacks can easily do damage in the teens. While first level characters should be relatively fragile, I don't think it's too much to ask that they be able to survive one non-critical hit, maybe two, before dropping!
[Edit] Some of you might be thinking, why not just reduce spell damage? No, the damage of 1st level spells is fine right now. If their damage was reduced, they'd be weaker than basic at-will weapon attacks, and that would be ridiculous. They'd also be weaker than cantrips at higher levels. I've suggested that they change cantrip scaling to match cleric and rogue deadly strike (2[W] at 9th level and 3[W] at 19th). If they followed this progression, cantrips would still be a bit weaker than 1st level spells even at 19th level. If you nerf the 1st level spells, cantrips end up getting better, and that's a bit absurd. Even if you did nerf the 1st level spells, it does nothing about regular weapon damage, which can still easily do damage in the teens. The most simple and elegant solution is to give characters more hit points.