I also think etonbears has it right, I love having options open. And I'm curious now, what kind of plans do you have? Do you plan it out attack by attack or just a general strategy of hitting a weak point?
Actually when I spoke of planning I meant in a very strategic sense, planning how I intend to approach the game overall, how I intend to develop my main character, then also my party, both the individual companions as well as the party overall in terms who's going to cover what party functions, etc. If at all possible, I even map out ahead of time exactly how I will be leveling up my characters (P:Km is set up excellently for this; the PoE games a little less so but still also pretty good).
At the tactical level of an individual battle, firstly it starts with how I have set up my party, and then gets down to the level of each individual party member and their functions. So with a party of six, I usually set it up as a main battle line of three up front consisting of my tank in the middle and two mobile dps flankers including my PC. A dedicated archer (may be rogue or ranger type) sits behind this line and shoots at the most dangerous of the enemy's casters. If I have pets or summons, they also sweep around the sides for the rear of the enemy. But my archer can quickly switch to melee if the enemy manages to get behind my line. Then I have two caster types of my own, one arcane and one divine, with the arcane focused on offensive or crowd-control spellcasting and the divine on buffing/debuffing or healing spellcasting. The arcane caster will also be able to switch to missile combat if necessary, while the divine caster can switch to second-line melee if necessary. If party size drops to five, the dedicated archer gets cut. If party size drops to four, specialized party roles become impractical, and the optimal party setup sadly degenerates down to four generic and boring jacks-of-all-trades.