Freshwater isn't that hard cobguy, the usual mistakes people make is not cycling the tank first to get a biosphere happening, and then adding too many fish at once which disrupts the biosphere causing ammonia levels to spike, or having too many fish for the size of their aquarium. Once you have a tank going, it's pretty smooth sailing with freshwater, it's once you get into the big tanks it can get more stressful, but also more rewarding. I'd suggest something like a 35-40 gallon for a beginner, small tanks can also be hard to maintain. 35-50 gallons is an ideal size to have a good tank. Also choosing the right groups of fish. I'm sure there's enough guys here who could walk you through it successfully should you try again.