My group and I are playing Curse of Strahd. During our most recent session, most of our characters barely managed to survive and kill the three hags at the windmill. My character is a Level 3 Battle-Master Fight that duel-wields when he fights and has +5 to hit with his melee weapons. During the entire battle I missed most of my attacks that I made. There would be some turns where I couldn't get a single hit in. I know that most of this is down to pure luck, but I can't help but to be frustrated about it. Besides going to buy a new set of dice, is there a way I can try and make it less frustrating when/if it happens again or do I just have to grit my teeth and keep rolling?

Grit your teeth and keep rolling, but also, don't think too much about missing just as you roll the dice. The universe have a tendency to land you in bad dice scenarios the more you think about them.

If you are in melee, the best thing you can do -- if the DM uses the flanking rules -- is to pair up with another melee fighter and get yourselves a flanking bonus. You have to be on opposite sides of the enemy to do this, and if so, then by the optional flanking rules, you will both get advantage on your attacks. This will greatly increase your chance of hitting.

The only other thing you can do, which is going to be tough as a melee fighter, would be to find non-attack-roll methods of doing things to the enemy. As a silly example, in a room with a lot of large furniture, you pull down a wardrobe on an enemy and the DM rules the enemy has to make a DEX save to avoid the furniture falling on him and knocking him prone. Such things depend on the circumstances and DM rulings, but that would avoid you having to make a to-hit roll against a high-AC enemy and then once he is prone, again, you have advantage. However, not all DMs are going to allow such shenanigans and may rule that you cannot do any attacks that are not listed on your sheet (and toppling furniture is not on your sheet) so this is highly DM dependent.

Additionally any types of buffs spellcasters can give you will also help. For instance if the cleric goes before you in the initiative order and fires off Guiding Bolt, the next attack gets advantage. Heck even if he doesn't go first, you could (if the DM allows it) "hold your attack action" until you "see guiding bolt hit". This would trigger your attack as a reaction to G.B. hitting and you would have advantage, since it is the next attack after the bolt hits. Similarly spells like Bless can help you. But you'll need the cleric or other person who can cast it to lay it on you.

Thank you guys for the advice.

Learn the advanced combat techniques and utilize them with ruthless efficiency. Flanking is just the start. For example, as a Battlemaster, if you use a maneuver to knock a creature prone with your first attack then your second attack has Advantage. Look at ways to keep them Restrained to really screw up their ability to dish out damage all while making them even easier to hit by giving you Advantage. The thing you should be building towards is how advanced combat options interact with your feat and maneuver selections. A Battlemaster is a combat commander, so also look at how you can assist the rest of the party or impose hinderances on the enemy. It’s not just about how much damage you do but how you can make everyone else perform at peak output.  

All you're doing is failing. When you fail at anything, accept that it's part of the process, grit your teeth, and keep moving forward. In this case, just keep rolling.

Or put the dice in the freezer.

Also you have to accept that sometimes the dice don't go your way. Sometimes you have a bad night with the dice. It happens.

Bad dice nights happen to everyone, this is true. Some people have it way worse than that. A buddy of mine can’t roll worth a dang to save his life. Dice, RNGs, doesn’t matter what it is because he is going to get hosed. One night I watched him fail to roll above a 6 on a d20 the entire night. As long as you’re doing better than that you’ll be okay. 

Also, sometimes you have to line up all of your dice and pick one at random to smash with a hammer as an example to the rest of those traitorous good-for-nothings. 

Yeah we had a friend like that, named Rob. No one would let him touch their dice -- we were afraid he would visit whatever curse he was under upon our dice, LOL. 

In Champions, the worst you can roll to hit is 18 (triple 6s on 3D6). It's like rolling a Nat 1 in D&D, only much worse... Nat 1 is a 5% chance, so getting more than one in a night, if usual, is still within the realm of possibility without being kinda nuts. One night, Rob rolled an 18, and I kid you not, three different times. The third time, people actually moved away from him in the room. One guy put up his fingers in a cross, like he was warding off a vampire. 

For those wondering, the chance of rolling an 18 is already 1/216... rolling 2 of them is 1/216^2, and rolling three is 1/216^3, or about 1 in 10 million. Now, it's not exactly that low, as he made several other rolls on 3D6 that night. But still... it is the only time we ever saw anyone roll 18s that many times in one evening.

In Champions, there is a Disadvantage called "Unlucky." Each 1d6 of Unluck is worth 5 pts, for a max of 3d6 of Unluck at 15 pts. You can use it to get points for your character. Whenever luck might play a role, and particularly if the character is doing well, the DM is supposed to roll 1D6 for each d6 of Unluck, and each 1 produces a "level" or rank of unluck that happens to the PC.

We used to say that in real life, Rob had 17D6 of Unluck. ;)

Had a session last night where I did 6-8 attacks in a fight. I hit twice. I had a hit chance of 55%.

I have also yet to do get a critical hit in the entirety of the campaign. We're almost level 5 and I'm a fighter.

Don't forget about ways you can inflict the Prone condition on enemies either through the shove attack or by grappling someone and wrestling them to the ground, which most DM's I've played with will allow. Melee attacks against Prone targets automatically get advantage. 

I'm running Curse of Strahd and had the same problem for one person, he was really unlucky with his roles.
I tried to help but the dice roles were just terrible, but these things normally balance themselves out.
In our last session the same player rolled really well and killed all of the enemies himself. He was a wrecking machine.

Its frustrating when its not going your way, but stay with it :) 

The top three Battle Master Maneuvers are Precision Attack, and there's your better chance to hit, Riposte so if they miss you can use your Reaction to take another swing at them and add to the damage if you hit, and Trip Attack so you can knock them prone and give everyone Advantage.

Yeah, it's really frustrating when the dice are not kind.  I've been there myself many times.  At least you have the tools to better your odds.

Someone on the Ironsworn discord recommended a strategy to prevent bad die rolls... Tell the dice you are "considering buying them" rather than that you own them. Dice always roll better when they think you might buy them.

You may have to keep them in a box when not in play so they don't realize they are living in the same house as you....