Not sure on the click macro's for a DK.
If you're playing all of the same, you can put the most common spells in the same slots on each.
And then spam them together.
Generally manually clicking is superior in pvp to using a /Click.

That said...

You can use two Blood runes, two Unholy runes and two Frost runes immediately.
And they will gradually refresh.
You will build runic power while in combat, and have some rune power dump abilities.
There are Death rune abilities, which convert say a Blood rune into a Death rune, which lets you use another Blood rune now.

So you'd want to prioritize (most damage first) your powers for the spec you're using.
And put them in a simple sequence, or maybe list them one under the other.
So you have the most useful at the top and the least useful at the bottom.
Then go through and check which runes each will use.
Adjust their position, so the runes used is not an issue.
Then you have the final order of abilities.

Next look at both the duration of dot type effects and the reuse delay of abilities.
A dot type effect can generally be cast immediately and again and again.
Other things cannot be cast more often then once per x seconds.

If it is a dot effect, you'll generally want the reset to be =target.
And for the comma's (delay) to be long enough for the dot to run its course.
With an ideal refresh just as it expires.

Those abilities with a reuse wait time, will generally be reset=combat.
Because even if you switch targets the macro cannot fire the next use until the cooldown is done.
As an example...

/castsequence reset=target Flame Shock,,,,,,,,,,,,,,,,,,,,,,,,,,,

--and--

/castsequence reset=combat Lava Burst,,,,,,,,,,,,,,,

Flame Shock can be recast long before the duration of the dot is done, but you want the dot portion to run its course. Lava Burst cannot be cast until 8 seconds go by. Except you adapt it to the DK abilities.

A great source for ability durations etc is wow wiki.
Do a google search for "Wowwiki +Abilities +Death Knight".
Or another class.
Then check the duration/recast delay on each ability in question.
Don't forget to factor in glyphs and talents.

You will need to know your spam speed per second.
And then include comma's equal to the seconds of delay you want.
With as many comma's per second as your spam speed per second.