Thought this might help. I could have used it when I first got into this hobby.
A word of warning: starting a marine tank cause a serious change in human behavioural patterns - looking dreamy eyed at your tank for hours on end; phoning your loved ones (or anyone!) in the middle of the night to tell them about a new polyp, worm, glowing thingy about 1mm long, ... which you have just discovered; not buying new clothes, furniture etc. because your tank REALLY needs that new light, filter, ROCK, etc.... Oh well, maybe you won't get hooked so badly.
Firstly, get some advice.
Most people’s main source of advice is the Local Fish Store (LFS). Petshops, LFS's, call them what you like, these shops all exist primarily to make money. If they do, they are successful, and the owners can live in comfort (or even grow rich ??). If they don't make money, they go bankrupt. They will always try to sell you the most expensive (often quite useless), items, preferably something which you will have to upgrade later (another sale for them...). And these are the good ones - the bad shops will also sell you incompatible livestock, or diseased fish, or even fish caught with poisons, knowing that they will die after a few days. They can then blame it on you (bad water quality, wrong filter..."you also need this UV steriliser to reduce disease..." and because you are not sure yourself, you inevitably buy more equipment (usually also useless). Get the picture..?? So BUYER BEWARE!
People on Internet discussion groups do not have any financial gain by what they recommend, and are usually impartial, but there is another problem lurking - Pride. "I use skimmer xxx, or pump zzz, this is the best, use it!" "Oh, I've kept 10 types of Angels, and 4 types of Damsels in a 50 gallon tank for the past 5 years, It’s EASY - you can do it too..." or even worse, "Oh, I am very successful with keeping anemones. They are easy to keep, I've had 5 in the last year..."
Advice in books is usually outdated. Details on the animals and plants tend to stay relevant, but "technical" issues such as filters, skimming, lighting, etc. tend to change rapidly, as new equipment and techniques are developed. So, before you decide on anything technical, query what the books say!
Whilst gathering your information, you must THINK. Is it logical, does it agree with what other books say, or with the views of "experts"? You must also get as many recommendations as you can, and then try to decide what is right FOR YOUR PARTICULAR SITUATION. Even some of the most notable "experts" on the net, some even with PhD's, can't agree on "what is right" all the time. They do tend to agree on the basics, though, so if you get some "way off" advice, you should be wary.