things to get first:
-water conditioner to remove chlorine and heavy metals in the water
-heater (an adjustable one will be worth the money)
-a few variety of betta food
-a thermometer for the tank
with a 1.5 gallon tank change the water 100% at least every two days.
Some say that water changing is stressful to fish, but in my experience here is the least stressful way to go about it:
Unplug heater, lights etc.
Scoop your betta in a cup. I use a small tupperware container with holes pokes in the lid for air.
Rinse decorations with warm tap water, set aside on a clean towel
Pour old water out
Rise inside of tank with warm water
Place decorations back in tank
Slowly pour in the water you let sit for 24 hours
Say, for a 3 gallon tank, only pour in 2 gallons
With the last gallon try to match the what the water temperature was before you started the water change with tap water (you will need to play around with this to know exactly how much warm water to add)
Add your water de-chlorinator
Plug heater, light, etc. back in
Pour the betta back in
i made a blog about my fish and all i got to is a betta fish check list kind of thing so if you would like more info you can check this out