There are lots of macros that you can use in UO and UO Assist. If you don't have it, get it. UOA is worth the $15.00 USD.
http://tugsoft.com/UOAssist/default.asp and is also a UO approved utility.
First lets look at some defensive tips and macros.
* Casting Heal - When you are a mage and trying to heal yourself, use "Heal" over "Greater Heal" for a few reasons. It will not be interupted like greater heal. Uses less mana and can be casted faster.
Most of my spells are in UO macros and then I use the targetting queue as DevilSpawn mentioned above. This way I have a little more control over the timing of the spell. You can also have a spell pre-casted, run back into battle and hit your last target key.
* Recall Home - This is the get the hell out of there tool. Using UOA, select a blank macro and hit record. Then open your rune book and click the diamond that will take you home. Hit stop on UOA and assign it a key or key combo. For this escape, I will burn a charge on my rune book even if playing a mage to keep from getting interupted.
This tool is also useful when you are running around making lots of trips back to your house.
* Chug a pot - Cure, Heal, Total Refresh. Again UOA has these already built in, just waiting for you to assign a key or key combo. Click the "Keys"Tab on UOA and look for Disarm, Disarm Left, Disarm Right, these are also waiting for you, along with arm, arm alternate, etc.
* Hiding - Nearly every character can use the hiding skill when inside or next to a house. This should work 100% of the time as long as you are not in line of sight with your attacker.
* Magic Trapped Pouches - I dont know if this still works, but we used to cast magic trap on small leather pouches. When paralyzed, open the poch, it will explode and break the para. You can assign a UOA macro to use item type.
Most of the offensive tips or macros are simply finding the right combo for your fighting style and particular opponent. This may be outdated, but I would usually run into battle with Mindblast or Exposion precast giving me a target cursor. I click the opponent, cast my next spell, and use the last target queue.
As DS mentioned above, most solid pvpers have their spells, special moves and targeting macros assigned to UO. They use each and every one of them.