If you are thinking Fish creek park I am assuming the west side although there is good fishing to be had on each side.
If you come in on the west side though I personally like to walk south as there are a few good spots that way.
As it is your first time out this could also be nice if you are right handed. The reason I say this is you can cast parallel to the bank which will give you lots of room behind without fear of snagging. Although any spot with lots of open room behind you will be fine for casting practice and there are plenty of open areas.
Just remember to be patient and make sure to watch your line especially if you are going with 2 flies. On your backcast make sure to give it lots of time for the line to straighten out or else you will spend all day untying your flies. Another thing, keep an eye on your line while casting, if you do tangle on yourself and catch it early then you can usually fix it quickly, if you don't notice it and you have a big mess of stuff you are just best to cut it and setup your rig again. I like to take a zip loc bag with me to hold the line when I do that as I try to keep the river clean.
Also if you find you are having some issues with 2 flies I personally found just casting one fly to be easier and a little more forgiving so don't be afraid to give that a shot if your patience is wearing thin.
Also I did notice some fish rising last weekend so keep your eyes open. I am not sure I would recommend switching to a dry fly at this point as they were rising pretty randomly but it would be a good indication of where fish are at least.
Hope this helps.