Keep the same set of rules for the medium to long term, only refining certain things to make steps forward in the quality of racing.
I'd like less dependence on technology, gadgets and fads: break-by-wire, DRS, complex energy recovery systems that reduce the direct car-driver connection; more go-cart, less Prius...
Either 2 or three well-differentiated tyre compounds that can be pushed hard for the duration of their window or only one type of tyre (with or without changes). Of course only one brand and no mandatory use of compounds (this should go without saying).
Refine aero at least to the point of reaching the original goals set for 2009.
Enough fuel to allow drivers to push as much as possible for a race duration.
No parc-ferme rules, excessive tyre limits, et. al > goal should be to let everyone qualify and race in the best conditions possible in order to maximize the probability of drivers racing on-track under as similar conditions as possible (mainly tyre and weight-wise).
Let drivers race, no TOs unless no mathematical possibility of WDC for second driver.
Less intervention by stewards if grass and gravel are brought back.
Allow smaller teams to be more competitive...