What are your typical chances to hit? If you are missing 70% of the time and you typically have a 30% chance to hit, then that makes sense. You should typically have a 60-90% chance to hit.
Typical chance is 35% -45% but that's not the issue. The issue is that the AI rarely ever misses. In any given battle the AI misses perhaps once. The AI also lands big hits on average, 6s and 7s to my 1s to 3s even though I'm one level ahead of them. The bosses I've fought can each one-shot a character from full health. I'll give them this, the AI is very, very good because you get that character up, and the AI immediately targets them again putting them down. This is leading to a situation were the party is wiped out before they can score a hit in some cases. I want to drive this point home. The issue is that the game is unbalanced. Either there needs to be a whole lot more healing ability or the numbers need looking at so the AI's hit rate is identical to the players because having a situation where the AI rarely misses and the player rarely hits is making this game unenjoyable.
Are you making use of Advantage? Ranged attacks from high ground and melee attacking the enemy's back grants Advantage which increases your chances to hit.
Where available, yes, but most of the map does not contain areas for height advantage.
What weapons are you using? Are you proficient in them? Are they making use of the best stat? Ranged weapons and finesse melee weapons are better for high-dex characters, all other weapons are better for high-strength characters. Using a weapon that your character is not proficient in (a different mechanic than str vs dex) effectively imposes a 15% to-hit penalty.
Swords/Mace and bows for ranged. Wizard aside, of course. My character is a fighter. The fighter was using a longsword, the weapon I start the game with because there is zero opportunity to upgrade weapons or armour. The fighter was stood next to a bog standard Goblin who had no buffs so I didn't even have to move, and my hit chance was 35%.
Are you often attacking with Disadvantage? Disadvantage is most often granted if the enemy is unlit and your character doesn't have darkvision, or if you're attacking from low ground. For the former, use torches or spells that grant light. For the latter, go to high ground.
Disadvantage in what sense? Give me a specific example.
What kind of spells are you using? Some are much better than others. Shadowheart's Sacred Flame, for example, is basically useless because it targets enemy's saving throws (and thus doesn't benefit from Advantage's bonus to-hit) and deals little damage. Some spells are guaranteed to hit, some require your character to make an attack roll, some target different enemy's saves. Some spells just deal more damage than others.
Flame Bolt, Ice Beam, Witch Bolt are my offensive spells. I have sleep (varies in usefulness), Grease, Mage Armour, Reflective shell and Thunderwave.
Are you using any types of buffs/debuffs? The Bless spell can help your characters hit enemies by providing a +1d4 bonus to attack rolls. Mirror image and Blur make it more difficult for the enemy to hit you. Potions of speed give your characters extra actions for a couple turns.
None of my characters have bless.
Edit: you just posted saying you usually have a 45% chance to hit. This is very low. See my comments above on gaining Advantage (adds 15-25% to-hit), not having disadvantage (which subtracts 15-25% to hit), and ensuring you're using proper weapons.
