Got any anxiety reducing tips from F-15 land Eagl? I do fine solo and dual, but toss a check pilot in the plane and performance decreases by like 25%. Fake myself out 
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Mission preparation is the first key. Walk yourself through the flight and keep yourself on pace with what is happening, based on what you *expect* to happen after doing your flight preparation. When something goes wrong or you have to deviate from the plan, either work to get back onto the plan or figure out what part of the plan you cut out and get back on track but maybe at a later portion of the plan.
For example, lets say you plan a training flight to a practice area for stalls, some VOR navigation with inflight cross-tuning practice, and a groundspeed calcuation exercise. Then you plan on flying into the class B to get some practice talking to the controllers on the way to a small airport under the class B for a touch and go or two, then return home for your full stop landing. But on the way to the class B, the controller says he is saturated so if you want to enter you need to contact FSS to air-file IFR, otherwise he can't take you. What do you do? You either orbit outside the class B while you go blah blah with FSS for 20 minutes trying to explain what you want to do, or you cut out that portion of your mission and do a few touch and go landings at your home field instead. The ability to make that decision on the fly (or pretty much any decision inflight) depends on the quality of your mission preparation. And realize you will almost never have a flight go exactly as planned, but if you have in mind what your priorities are and go through a couple of what-if scenarios before you take off, then you will be a lot more confident in dealing with events as they occur inflight.
Another thing that helps is to wiggle your toes. Seriously. Focused figeting
Any time you need to be smooth or precise on the controls, wiggle your toes. It is like magic for a lot of pilots.
Finally, cockpit setup can really help out. Having all the info you need easily available inflight can really reduce your workload. I had a cheapo clipboard velcroed to my leg using a velcro and elastic strap my Mom sewed up for me, with some elastic loops to hold 2 pencils (because one always runs out of lead right when approach is giving you your clearance). Taped to the clipboard was performance data for the plane (approach speeds with and without flaps, best climb speeds, etc) and the frequencies and identifiers of all the navaids, control towers, and approach frequencies I used in the local area (San Diego so it was a pretty long list). Then before takeoff I unfolded and re-folded the terminal or sectional chart to have instantly available my route of flight because there were multiple VFR corridors with altitude block changes and every flight I had to weave my way through them. So rather than try to do it by memory and then give up and have to unfold the map inflight, I just prepped the map to show what I wanted it to show. Some people went a step farther and just cut out the parts they cared about, and laminated them into an easily foldable oversized sheet. They had to update that with every chart revision, but the arts and crafts project took maybe 10 minutes every 90 days and cost the price of a couple square feet of clear contact paper...
Figure out what you use the most, and have it available. Then think about stuff you might need in a hurry (frequencies were a big deal for me) and make a cheat sheet. Keep that UP TO DATE with a note on the bottom "current as of" date otherwise some instructors or evaluators will ding you for flying with out of date information. Another thing some people do is removing the airport guide or approach plate for the fields they plan on landing on or flying approaches to, and putting them into small page protectors and putting them on your kneeboard. After the flight, put them back into the binder to ensure they remain up to date otherwise you'll lose them or end up flying with out of date pubs.
But as you can see, except for wiggling your toes it all comes back to mission preparation. Don't try to what-if every little thing and don't make your quick reference sheets overly complicated, but you can really reduce your workload and ability to deal with unexpected events if you have a solid preflight plan, know what your priorities are, and have an idea of how to get things done or adjust the flight if things don't go to plan. That can really boost your confidence and make you look a lot smarter when someone is evaluating you.
A story - on my PPL checkride, we were departing the congested airspace on the way to a practice area for maneuvers and stalls when the evaluator asked me to calculate ground speed by timing over known points on the ground. Well, darned if I couldn't remember at what point I was supposed to divide by 60 (or multiply?) to convert from seconds to MPH, so I spent 10 minutes digging through my flight bag for my inflight computer, pushing buttons for a while, and basically making a fool of myself. At some point the evaluator had enough watching me flail around and told me not to worry about it. After the flight when we discussed that little fiasco, he said he didn't really care whether I could calculate my groundspeed. He just wanted to see if I could do more than one thing at once, fly the plane plus do a little basic math and inflight planning. It turns out that I prioritized flying the plane high enough in my brain that I remained exactly on altitude and heading, and that sucked enough brainpower that I couldn't remember the simplest of inflight calculations. But he was satisfied that no matter how flustered I got (because I was pretty spun up about it while it was happening), I would continue to fly the plane FIRST and that's all he wanted to see.
So of course, just fly the plane first. Even if you get violated for flying in the wrong place, at least you won't be dead. After you focus on flying the plane, THEN you can use whatever remaining brain cells you have to navigate and communicate. But aviate navigate communicate is the correct order for your priorities, no matter what the situation is.
