tinker around with something like this. try removing chain lightning for a "boss all out single target dps macro" as its a waste of mana imo, regular lightning > chain lightning vs 1 target.

/assist party1
/castsequence reset=target Flame Shock, Null
/castrandom Lava Burst, Lava Burst, Lava Burst, Lightning Bolt, Lightning Bolt, Chain Lightning, Flame Shock

some people have said to use the below macro,

/castsequence reset=target Flame Shock, Lava Burst, null
/castrandom Lava Burst yada yada yada (same as the other one)

but i dont like having the lava burst in the sequence, just on random, because its such a long cooldown its rarely up just after killing trash and switching targets so the shaman will shock and then just sit there rather than spamming a lightning bolt or 2 before lava burst comes up again.

also another decent option is just purely using castrandom and hoping it keeps the flame shock up, overall it may be better dps but i like going a full run and seeing 100% crit with lava burst

example of macro without sequence;

/assist party1
/castrandom Lava Burst, Lava Burst, Lava Burst, Flame Shock, Lightning Bolt, Chain Lightning

theory behind having the same spell in there multiple times, has better odds of "randomly" casting it. not sure if its true or not but it sounds good to me so i use it.