Is there any theory or advice in how best to plan declarer play in a 4-4 trump fit. In what situations do you draw trumps, in what situations do you not draw trumps and any other advice?
Count, count, count; and when you are done counting, count some more. Count your tricks, count your losers, and count your winners; count the opponents' distribution and count your opponents' points and count your opponents tricks. When the cards have all been returned to the board you can start counting the next board. Until you are the best player in the world, and perhaps not even then, you can stop looking for more things to count.
In Notrump contracts you are advised to plan your play from the count of your tricks. Do this as Dummy comes down, as there is no point to a line of play that is not based on an expectation of sufficient tricks.
In suit play you are advised to plan your play from the count of your losers. Do not play from Dummy until you have a line of play for the entire hand that has an expectation of reducing your losers below 7 - (level of bid).
Contrary to the estimable Mr. Au, there is no magic formula for where to ruff or when. Esoteric plays arise from adjusting his rules to suit the need and count of a particular hand. There also is frequently a need to partially draw trumps when one needs to ruff, either for tricks or control. One particularly common scenario is to leave a single boss trump out and then cross ruff, forcing that opposing trump to over ruff a single trump of your own rather than a pair, leaving the other as counter to a loser elsewhere.
The advantage of a 4-4 trump fit is that you may use either hand for ruffing, and draw trumps from the other hand.
So the idea is to identify the hand with one (or more) suits that are shorter than the same suit in the opposite hand. Then lead "long" cards from the opposite hand into the short suit hand for ruffing. Use the trumps in the long card hand to draw the opposing trumps. The reason you ruff first is because if you draw trumps first, you may not have enough trumps left in the short suit hand for ruffing.