First you need to deside what you want in your tank..
Reef tank: corals inverts and fish (most of the tanks on here and my personal recomendation i find fish tanks to be kinda boring)
Fish only tank: like the name implies fish only
Specialty fish: for the more exsperinced reefer like a dwarf seahorse tank
next what type of filtration is right for me:
False back : alot of work and less tank room but class A filtration
Sump : not as hard to set up as a false back but you will need like a 5.5 gallon tank and in the event of a power outage some times a sump will over flow cause all the watter falls back down to it but Class A filtration
Canister : probly your best bet i like the fluval 105 persoanly realy effective and not wallet breaking exspencive Class B Filtration
Power Filter : Not recomended for a reef tank at all but will work for a fish only tank Class C Filtration
Corner/internal/sponge/undergravel: avoid at all costs but is acceptable for a quarenteen tank
Type of lighting:
MH(metal halides): The best lighting out there if you want to have corals or an Anem 1 150 bulb will cover a 10g great and you can have those beutiful corals that make the reef tank perdy
T5's: I personaly dont think T5's are good enough for sps even tho people say they are just as good i still hold some reservations
PC's (power compacts)/floresents: okay for a fish only tank you can MAYBE do zoas but i dont recomend it at all
To skimmer or not to skimmer?
a skimmer pulls the disolved bio waste out of the tank i would definatly consider one if you build a sump just avoid the fussion nano skimmer at all costs its a POS but there is other small ones that are nice just will cost you a bit
Live rock and live sand is a must even petco carrys live sand now i dont trust their live rock tho

idk just something about a chain stores live rock and the idiots they hire
make sure you check your salinity amonia ph nitrites and nitrates at least once a week ( eventualy i would spend the money on the pinpoint moniters i love them so much hung them on the side of the stand with velcro and everyday i log the readings) i hate the float salinity testers you always have bubbles on it and then your readings are never acurate and temp affects the readings too a refractomiter is much more acurate but the CHEAPEST one will cost you 50 bucks and you can get a pinpoint salinity monitor for what 115 USD and all you have to do is clean the probe every 3 weeks to a month.
If you do a reef tank make sure you get like 1 snail for every gallon and like 1 hermit crab for every 3 gallons MIN.
the coralife digital thermomiter is what like 10 dollars get it its worth it if you go up to a big tank i recomend the wireless pinpoint one cause you plop 4 sensors aroudn the tanks and get readouts from the sump deep water higher up and some place else
If your running MH you WILL STILL NEED A HEATER what happens to the water after lights out even if the heater is only running for like say 2 hours a day just b4 lights on that dip in temp is stress you dont want i recomend the visitherm stealth heaters
you might need a chiller but i doubt it
in a 10g you dont need a UV sterilizer unless you deside some day to do a bigger tank and toss a uv in there for the time being hey it cant hurt
I personaly only use air pumps in a sump set up i hate air bubbles in my tank with a passion tho my pump is battery backuped so i pull the stones out if the sump and plop it in the main tank
Starter fish:
Blue/green Chromis: Hardy nice coloration good personalty and will school in groups and to top it off they are CHEAP! (tho a 10g is small for an adult chromis they like to swim)
False Perc Clowns: everybody <3's the clowns
watchman goby: I cant say enough good things about this fish peaceful and a face only a mother could love some people dont liek their coloration but under nice lighting their blue spots will POP some times i wonder if when they where making sesame street and making oscer the grouch is someone had a watchman goby and got the face from him
so basicly thats my crash corse in saltwater tanks i know my grammer and spelling sucks but hey what can you do
THE BIGGEST TIP IS WHEN YOU GO TO THE LFS AND YOU SEE A FISH OR AN INVERT AND JUST LOVE IT BUT IT:
1: Is aggro
2: Its the (insert blank here) i have been looking but looks a little sick,thin,discolored
3: my tank is a little too small for (insert blank here)
4: I have never see that fish befor
LET IT GO! DONT BUY IT your harming the fish you bought the ones in your tank that your already hoplessly inlove with and your wallet
RESEARCH IS THE KEY TO THIS ADDICTION.