[h1]Primer: Chain Gauge and Battle Format[/h1]
One of the most important parts of FF13 battles is the Chain Gauge. This describes what the chain gauge does and how it and other information will be represented in the RP. 

The Chain Gauge is a passive modifier on all damage that a target receives. The minimum value of the Chain Gauge is 100.0%, and the maximum value is 999.9%. Every enemy has a Chain Resistance which modifies how quickly the Chain Gauge is built. Every enemy also has a Stagger Point. Once an enemy's Chain Gauge reaches the Stagger Point, several things happen. 1) The Chain Gauge immediately jumps by 100% (so if the Stagger Point is 120%, it jumps to 220%). 2) The Keep value for the target is reduced to 0, and nearly every action taken against it will interrupt the target. 3) The target often changes resistances. All targets are immune to Launch when not staggered, but some might be launched after the Chain exceeds its Stagger Point. Certain targets are significantly easier to defeat when staggered, and some are essentially impossible to beat until they are staggered.

Every action performed has two values that modify the Chain Gauge: Chain Bonus and Chain Duration. Chain Duration is a value that extends the length of the time that a Chain is active. In practice, these actions stabilize the Chain Gauge, slowing its rate of decay. When the Chain Gauge is depleted, the Chain is broken, and we start over at 100%. COM abilities are best at stabilizing the Chain Gauge, but SAB abilities are also relatively strong at this. Chain Bonus raises the value of the Chain Gauge. RAV abilities have the best Chain Bonus, but SAB abilities are decent in a pinch. Some abilities (specifically the -ra abilities in the RAV role) have higher Chain Bonus against staggered targets. Look for the S in the Chain+ column. 

Next, this is the table you will see during battles. This table has most of the pertinent information you will need for battles. It's about 99% done - only thing I'd like to add is a link to images for the enemies, but that could be done in the Libra section. Anyways, this gives you a ton of information: Enemy HP%, Chain%, Chain Break, Initiative, who's next, Paradigms and Roles, and Statuses. I intended to show off several different possibilities in the battle. For example, you can see that the color of your HP bar changes as you reach certain thresholds. Red HP is considered "Critical." Yellow HP is between 30% and 70%. There are a few modifiers that look at the HP% in these terms. You can also see TP. TP is used to cast Techniques. The first TP you get costs 20 points, the second costs 30, and the last costs 50. 

There's a lot of information in this table, but it's fairly condensed. Also in case you were wondering, this table is completely automated from my spreadsheet. Fun stuff.

[table=bordered][row][cell][b]Group A Battle![/b][/cell][cell][b]Current Time: [/b]2 sec[/cell][cell][b]Paradigm: [/b][/cell][cell][b]Delta Attack[/b][/cell][cell]Next Up: Noir[/cell][/row][row][cell]Nadia - [color=ed1c24][b]COM[/b][/color][/cell][cell] HP: {[color=39b54a][][][][][][][][][][[/color]]}[/cell][cell] Next: 5 sec[/cell][cell] TP: {[color=fff200][][][/color][color=39b54a][][][][/color][color=00aeef][][][][][][/color]}[/cell][cell] [b]Status:[/b] [img]https://i.imgur.com/HHhedk1.png[/img][img]https://i.imgur.com/k8gqw2C.png[/img][/cell][/row][row][cell]Noir - [color=fff200][b]SEN[/b][/color][/cell][cell] HP: {[color=fff200][][][][][/color][][][][][][]}[/cell][cell] Next: 2 sec[/cell][cell] TP: {[color=fff200][][][/color][color=39b54a][][][|[/color][color=00aeef]---------|[/color]}[/cell][cell] [b]Status:[/b] [img]https://i.imgur.com/ac4TEe4.png[/img][/cell][/row][row][cell]Julian - [color=0072bc][b]RAV[/b][/color][/cell][cell] HP: {[color=ed1c24][][[/color]][][][][][][][][]}[/cell][cell] Next: 4 sec[/cell][cell] TP: {[color=fff200][]-|[/color][color=39b54a]-----|[/color][color=00aeef]---------|[/color]}[/cell][cell] [b]Status:[/b] None[/cell][/row][row][cell]Barbed Specter [/cell][cell] HP: {[color=39b54a][][][][][][][][][][][/color]}[/cell][cell] Next: 10.5 sec[/cell][cell] Chain: {[color=f7941d][][][/color][][][][][][][][]} 120.5% [b]Break:[/b] 17.9 sec[/cell][cell] [b]Status:[/b] [img]https://i.imgur.com/C0rLRHN.png[/img] (Noir)[/cell][/row][row][cell]Breshan Bass A[/cell][cell] HP: {[color=39b54a][][][][][][][][][][/color][]}[/cell][cell] Next: 12.3 sec[/cell][cell] Chain: [b][i][color=f7941d]STAGGER![/color][/i][/b] 231.6% [b]Break:[/b] 17.9 sec[/cell][cell] [b]Status:[/b] [img]https://i.imgur.com/ZFZdHBz.png[/img][/cell][/row][row][cell]Breshan Bass B[/cell][cell] HP: {[color=39b54a][][][][][][][][][][][/color]}[/cell][cell] Next: 10 sec[/cell][cell] Chain: {[color=f7941d]--[/color]} 100%[/cell][cell] [b]Status:[/b] None[/cell][/row][/table]
Edit: Since creating this table, I have added a few features. One of the more useful ones is the Chain timer. Underneath the chain gauge (or the word Stagger) is an underline. This represents the time left on the Chain. If the underline extends to the end of thechain gauge (full), the chain will last for about 45 seconds. It depletes at a proportionate rate (at 1/3 full, it's 15 seconds, etc). I understand that the underline is a bit hard to see with the Chain bar in the way, but this should at least help a lot during Stagger.