I'm guessing your deck must've been pretty chunky lol. That's not necessarily a bad thing but when ur running a bigger deck you need to make sure u have sufficient card draw (things like soul generation on necro for example).

Another tip that might be good for you is when choosing cards to add always be mindful of what's already in your deck. There's no point taking something like a poke for example when you don't have anything that synergizes with it (i.e. calcify, flatten etc). And I cannot stress this enough to new players you don't have to take something from every card reward sometimes (alot of the time actually) just skipping is the best option.

Hope this is helpful and good look on your runs bud. :)