...Players like roleplaying and all, but there's also a thrill and fun in trying to struggle against the odds - if everything was predetermined as the player surviving one way or another any encounters, then, the feeling of risk and of your actions mattering in important situations would be considerably lessened.
The other thing I found out was that bad guys want to win too. Therefore, they generally do their damnably best to, even if it involves kicking you while you are down.
Therefore, seeing the fickle nature of combat most of my arbitrating in regard to determining if something succeeds or not is going to hinge heavily on the roll of a d20 (a twenty-sided die) on fixed numbers to beat made up in my head (generally being 0, 5, 10, 15 or 20) - the higher the score rolled on the die compared to the result to beat, the more effective the action will be as well.
You have no control over the dice, but you do have control over your actions.
Try to limit the content of your posts to something a character would manage to do under 10 seconds to respect fast pacing (long winded speech might not be good at all - telepathy is much faster, though). Try to post only once in reaction to my own posts if at all possible. Also, try to have your text depict one of the following: full-post movement, full-post action, or a combined move-action.
By spending your time moving, dodging and weaving to avoid hits, my difficulty to try and hit you will be higher. Just the same, if you concentrate on just attacking and don't move much, your accuracy will probably go up for it. If you fire many weapons in a post compared to firing just a few, your accuracy will suffer the same way because you are trying to do many things at the same time, firing a moving target is more difficult especially if you are moving yourself.
You have tools which make some things easier to pull off. Firstly, your AIES units will automate some of the things like nodal drones/bits - it also takes just one word to tell the AIES to launch counter-measures... and well used countermeasures can save your butts while allowing you to do something else. Secondly, you have shields you can quickly use to defend. Your AIES will also lock and launch offensive missiles automatically, meaning you can spend your time doing something else (if reasonable) after assigning targets and telling the AIES to fire. If you are stuck trying to dodge attack, nothing prevents you from using that time to reload your weapon or to charge your forearm weapon to make a more effective charged shot later. Melee attacks will generally be easier to deliver than ranged attacks. Grouping up on one target will make it harder for that target to take into account many attackers and so its chance of evading diminish some...