Just take it slow and easy. Being your first time the odds are good that you will spill some water. I always lay down a large towel when I siphon water out and into the tank to soak up spills. Im also wary and careful not to get any of my neons in the siphon suction area!
For the replacement water from the tap I put it in a bucket the day before and let it sit until the next day. Then if the bucket water temp is a lot colder than the tank temp I temperature match the new water with the tank water by mixing in hot water in with the new water and giving it a good mix, continuously checking with thermometer. Put in any liquid fert for your plants (if you use liquid fert) into the new water too and mix well.
Lastly after all this I add Prime water conditioner into the new water mix it well and let it sit for 10mins. Then I siphon it into the tank.
Pretty easy.