Eventually I didn't make everything horizontally or vertically, I just made sure everything was firm. I like the outcome though :D
As you can see I went criss-cross with the V to make sure every part was covered.
Here are some problems I ran into while making it:
1. The letter O was quite difficult to make and the rest of the letters...I'm sure they're not straight.
2. Cutting it with scissors wasn't the smartest idea.
3. My cardboard was kinda thin so it would bend when I wrapped the yarn over the longer parts because I tied the yarn pretty tight.
4. Some letters are difficult to wrap, for me the hardest was V.
What I'd recommend:
1. Print the letters out and glue it on the cardboard so you can cut it out easier and straighter.
2. Use a rotary cutter, box cutter or something and a cutting mat.
3. Use two layers of cardboard or use letters you bought somewhere. Just make sure it's firm ;)
4. Glue some little pieces of yarn on the parts you can't wrap easily, go criss-cross or cut some part of the cardboard off. I ended up cutting the tops of the V so that it was the same direction of the yarn wrapping, that made it a lot easier. Just play with it and you'll figure something out ;)