my first venture into saltwater I had a 30g salt water tank, the store I got everything from was a joke they first told me not to go into saltwater that it is way to hard and expensive (first off what hobby isn't somewhat expensive, second what kind of store deters a potential frequent shopper?) Anyways they were reluctant to help me out, they basically handed me salt, told me to go to meijers to get water from the culligan machine and that I would need this magic bottle of aquasafe to make the water safe then just dump the fish in the water after 2 days of waiting and I would be good and as for lights I would only need a crappy 2 bulb system that had barely any light output. Well you can see where this went, I had rock, light, water, sand, and aquasafe... I set it up and after two days I put fish in and did I mention they sold me the fish too? 2 clowns, some weird blenny, coral beauty, tons of snails, blood shrimp, and I think they sold me a tang as well, cant remember the exact one, oh and the skimmer was a crappy one rated for like 20g of freshwater. Well everything by surprise lived for exactly 3 weeks, the first to die was the tang, hmm interesting the one whos most sensitive to ammonia dies first, then the 2 clownfish which I started to tear up at that point and a day or two later the coral beauty died and I had it. I didn't know much about salt water and I depended on the store to help me out which they did not, I looked up more online and more on maintenance and found out about a thing called cycling, and water changes and forums where I could get help, well the only thing that survived once I started doing water changes was my blood shrimp which I still have to this day
My little bit of knowledge for people is make sure the people selling you stuff actually care... and for newbies I tell them forums make the world of a difference because there is always someone who has already gone through what you have had happen to your tank and they can help.
And I forgot to mention I did not have a job at the time, this was after saving up tons of money to get started, and after things died I had no money but my mom was nice enough to give me the money for free! And she was also good enough to loan me money to get my 120g up and running through mini payments, christmas and bday money I paid her back.