I like the following set of agreements with my 4SF auctions that I think make it very playable.
Allow opener to freely bid responder's major with two card support on the 2 level for his third bid. I always see people discussing things like what is the "default bid" on auctions like 1
♦ 1
♥ 1
♠ 2
♣, and it drives me crazy because there shouldn't be one! Opener should just be able to bid 2
♥ on a doubleton.
Always remember the overriding principle with extremely few exceptions: It is responder who sets trumps. There can be no confusion as long as you remember that. Ken gave the example of 1
♦ 1
♥ 1
♠ that responder might bid 2
♣ with a variety of intentions. I agree, but frankly it doesn't bother me as I think there should be no confusion. If opener bids 2
♥ now, responder's bids of 2
♠, 3
♦, 3
♥ all set trumps, 2
♥ did not set trumps. Simple.
In conjunction with the above, I like to play that bidding then rebidding the 4th suit is still artificial (though it tends to show some length there, else you would have a clearer idea where you are going) whereas immediately jumping in the 4th suit is natural 5-5 game forcing. So 1
♦ 1
♥ 1
♠
3
♣ is 5-5 clubs and hearts, GF.
2
♣ 2
♥ 3
♣ is still doubt about what strain to play, maybe 3433 with no club stopper.
The last thing I would say is on opener's 3rd bid, tend toward the cheapest reasonable bid when nothing seems good. Not only does this leave responder with the most room possible most often, but it means opener's higher bids are more descriptive (as they deny the ability to make lower bids). So on the 1
♦ 1
♥ 1
♠ 2
♣ auction, as opener I would generally bid 2
♦ with 4252 or 4153 even with a club stopper. The auction might continue 2
♦ 2
♥ 2NT, which it's easy to see is both lower and more descriptive than 2NT 3
♥ 3NT.
I have other more complex and artificial suggestions that I believe help a lot, but I think the most gain won't come from a system overhaul (well maybe, since you use a 12-16 NT

) but just from a clear understanding of the principles that will help make these auctions easier and more descriptive.