Decide ahead of time the type fish and study them. IF you are considering Koi invest in a good net or two. I prefer one very large net 24" across or larger, and a smaller sock net more moving fish. Neither is cheap, but well worth the investment. If just goldfish a 12"-18" net will be fine, long handles are a plus!Liquid drop test kit, Which needs to include, ammonia, nitrite, nitrate, PH, KH and GH at the least along with a thermometer. A couple of NEW clean 5 gallon buckets and a tub or cooler for transporting and acclimating new fish and rinsing plants, decorations, etc. mark them as POND USE ONLY. no chemicals, or fertilizers, or other foreign matter to go in these. You will make use of them many times.!!! Also invest in good water dechlorinator/water conditioner. be sure and check with your local water company and see if they use Chlorine or Chloramine to sterilize the water and buy accordingly. Have enough on hand at all times to treat the whole pond in case you leave the water on and over fill the pond or have a emergency late at night and need to do a large water change.