Armchair flying works wonders.
Do your flight plan first, then set yourself up in a chair and pretend you're in a cockpit.
Run through the whole flight, from engine runups, to getting your airways clearance, to taxiing, takeoff, and climb. Pretend you're holding a control column, and actually turn the thing left or right, to get the plane to go the direction you want. Use your flight plan, use your maps, and visualise the whole thing. Look at your maps, and if you're supposed to fly over a mountain, visualise it. If it will pass to the left of you, pretend you can see it. If your first turning point is 5 minutes away and you turn left to a heading of 220, go through that in your head. Imagine what youll be seeing outside, and imagine what you have to do in the cockpit to achieve it. Pretend you can see the DG.
Go through the whole flight, following your position on the maps, and you'll soon see if your map system is working, and if its not, youll know what you should do to improve it. A lot of it at this stage is trial and error - but it will save you a lot of money, and a lot of frustration, if you can do this trial and error without the aeroplane engine running.
If its a bad weather day, go out to the airport anyway and ask your instructor if you can sit in the cockpit for an hour or so. That way, you can actually move the control column, actually move the fuel tank selector, actually press the PTT while you make your 'radio calls'. (just keep the master switch off
)
As for cockpit organisation, I prefer to have my flight plan printed in a landscape orientation on a kneeboard that is also aligned landscape across my knees. My maps I put underneath, but pre-folded to display the part of the map I need, and only what I need, and sequential maps are in the pile in the order I will need to use them for the flight. VTC, then VNC, WAC, then the VNC and VTC for the destination. If I'm done with a map for the rest of that flight, I either put it in the map pocket by my knee, or on the seat (yes, I sit on it).
Keep a couple of pencils pushed into a Terry Clip attached to your kneeboard. Some people like to keep their pencils on string, so if you drop it you can just pull on the string to get it back. I like to keep a spare pen or pencil in my pocket as a triple redundancy, too.
You might like to invest in an A4 size clipfolder instead of a kneeboard. Fold it inside out, so the clip is on the front (and there you clip your flightplan) and the inside of the folder makes a handy place to store maps. This way, everything is in one place, and once you join the circuit area at the destination, you can take the entire folder and put it between the seats (or even on the back seat), and you now have a sterile cockpit with nothing to get in your way for the landing.
By all means carry the full ERSA when you fly, but I recommend printing out the pages for the places you know you'll need - and putting them on your kneeboard too. Keep them in the order you'll need them - its much easier to look at a single piece of paper, than try to balance the whole book on your lap.