Their are many factors which seperate the average players from the good to the great. The kind of Factors involved are aim which is a pretty obvious one, experience, knowledge, setup and in my view which is one if not the most important is a players strategy.
When it comes to strategy a player who is a relatively new to gaming, well even still alot of the old skool players use very little tactical wit in their game play. But over the course of a long time the usage of tactics can help bring on other skills making them a better players. Now you maybe asking me what do you mean by strategy, well an example would be the strategy demo I made under the strategy section for quake 3. I did a strategy demo for the map q3dm13, where it basically was showing me playing a bot and controling the key items on the map, now that is a very imporant factor when developing tactics for a map, each map in turn will have it's own tactics because of the variation in the items and their placements, this is one major factor in why some players do well on some maps. It is like this real life warfare were some forces are more suited to some fighting conditions. But Like real life warfare which side has the tactical advantage will usually win.
Planing
Well you may now see why tactics can be helpful in game play. But then how do you go about creating tactics for the various maps and remembering all the different times when things spawn back. Well from when I started to practice tactical play the idea took along time to adjust to, but it helped my competitive game greatly, although with tactical play practice is very important. Anyway when creating tactics their are a few things you need to consider about the map in question. To show you what can be involved and what needs to be considered I will use q3 tourney4 as a example.
Items/Powerups:
Red Armor (every 25 seconds)
Mega Health (every 2 minutes)
Once you have laid out what items that are on the level you will need to priortise each item on their importance, q3tourney4 is a relatively easy map to create a tactics because it is about controling the powerups being the main objective. And since their are only two items/powerups this makes it easier and gives you more time to control the situation but it can also give you alot of time to spare which needs to be filled in usually by hunting down your opponent. This idea from map to map does not really change, controling armor and powerups is still what you need to do to control a game.
Timing Items
Now remembering when various items and powerups respawn can be abit of a problem, this is why the experience and practice is important as you will begin to get a feeling of when things will respawn but with a strategy you will set out so that you can be at the spawning site of the idea prefectly when the item respawns. Usually what is done is a certain map rotation is used that may take say take around around 30 seconds going around various points on the map ( give or take 5 seconds ), and the red armor on tourney4 is the start point for the rotation. So if the Red armor spawns every 30 seconds you return to get the armor and every 4th time you pick up the red armor you would go to the mega health, simple as that.But problems can arrive when items get out of sync a good way to help you get back into a flow is delay some of the rotatiosn or (strats).
When it comes it other maps it becomes more complex with more items and powerups to control, but when it comes down to it, it is first getting the fastest powerups and then bringing the later spawns into the pattern into the strat and again it is important to try and get each item into a "universal spawning time to help make the tactics more effective and deprive your enemy of the items.