This is a very good question, and here’s some general tips about planning a trip, and some specific advice for you.
I’d approach it 3 different ways
1. Get a general sense of what to expect based on type of stream, location (region) and time of year.
2. Research major hatches you might reasonably expect to run into
3. Get up to the minute advice on stream conditions from a local fly shop about flow conditions, specific hatches (where, when, specific patterns/sizes that are working)
So as an example of general stuff, since you’ll be fishing Spring Creek, which is an actual spring creek, there are certain food items that are available to trout all year like Scuds, Sowbugs and Midges. Since you’re fishing in June and moving into summer, terrestrials like Ants and/or Beetles would be good searching patterns to add to your box now for any stream in PA as well as some hopper patterns for August you can add later. Expect water flows to be less than early spring and water to be a bit clearer so trout can be holding in different places that had too much current earlier in the year on the same stream. On really sunny days, you might try casting to shady areas near the bank out of direct sunlight, as well as the usual places like current seams etc. Some of the flies can be small, and the water clearer, so going to a longer tippet in 5X or 6X (instead of smaller sized tippet) might be needed to get better presentations (and you’ll break off less fish than going lighter).
As far as major hatches, for June and into summer in PA, there are several light colored mayflies that you should be ready for since they’re pretty widespread. Sulphurs (size 16 and 18), Light Cahills (size 14), as well as standard patterns you may already have that match hatches like Blue Wing Olives (size 14-20 BWO or Adams) and Blue Quills (18 Adams or Blue Quill) and Tan Caddis size 16. In addition there are some specific hatches that are less reliable, but catching one is like the “Holy Grail”. The Eastern Green Drake happens in slow water silty stretches of many streams in PA in the first week of June, usually right before dark. Specific, locally tied patterns from fly shops (a lot of the ones sold on-line match the Western Green Drake which is a different color and smaller) are “must have” flies for PA . ( I carry Epoxy Back Green Drake Nymphs and Green Drake Snowshoe Emergers size 8, and Extended Body Green Drake Parachutes and Extended Body “Coffin Flies” ( a large white fly that imitates the EGD spinner) in size 8 and 10. There are other hatches like Tricos. Isonychia (aka Slate or Mahogany Drakes), Yellow Drakes etc that may also pop up later in summer or on other PA streams. You can get a general sense of PA hatches by googling for hatch charts online. Here’s a link to a hatch chart for central PA Hatch Charts
As far as specifics and zeroing in on a specific stream on specific days before a trip, the best way to go is to get up to the minute info from a local fly shop to get info on stream conditions and hatches. For Spring Creek you might want to check out stream reports (for up to the minute conditions) and the month by month hatch chart (to get an idea of what to expect a couple of days in advance) and then pop in to get up to the minute info, some tips and a few recommended patterns for specific hatches from this local shop: The Feathered Hook Stream Reports
If you tie, good easy to tie searching patterns for PA are Green Weenie 12, Walts Worm 10-12, Ants or Beetles, Soft Hackled Wet flies like Partridge and Green/Orange 14, Pheasant Tail Nymphs 16-20 (for Blue Wing Olives, Blue Quills and Sulhers), Light Cahill Nymph (or cream colored Hares Ear) 12-14 (for Cahills)_ and size 8 for EGD nymphs). And if you’ve got some tying chops you can tie up stuff like Comparaduns or Sparkle duns to imitate specific may fly hatches and Tan X Caddis. These dry fly patterns use fine deer hair (sold as “Coastal” or “Comparadun“ hair instead of expensive dry fly hackle) in various sizes and colors to match the naturals and are pretty easy to tie once you’ve knocked out a few and can be very effective.
If you want to see pics of the naturals, and to learn more about specific hatches and best time of day to catch the hatch, how to fish them, a site like Troutnut.com Fly Fishing for Trout
is a great resource. And you can always ask questions here on this forum for tips on fishing different hatches.
As you spend more time on stream, a good thing to do is to start keeping a log—not only of what you catch, but dates, time of day, section of stream and what you see so that you can know what to expect from year to year.