You're telling it to cast on your mouseover *and* on yourself (player) in one set of conditionals. Also, help implies exists, so those are redundant, and @ is the same as target= just shorter. Actually, you're basically wanting to cast Nature's Swiftness and Tidal Force each time you press the macro. If your mouseover doesn't exist, you're saying to cast them on yourself (but they always get cast on yourself, since they're self-buffs). Finally, you're telling the macro to cast Healing Wave on your mouseover if it exists, but then not do anything otherwise. An empty set of brackets for a conditional tells the macro to cast the spell as normal.
#showtooltip Tidal Force
/cast Nature's Swiftness
/cast Tidal Force
/cast [@mouseover, help, nodead][]Healing Wave
Use this site to get a quick explanation of what a macro does:
http://www.macroexplain.com/
That site actually says that Tidal Force invokes the global cooldown (GCD), which means that the macro I posted above still wouldn't work. However, Wowhead says that Tidal Force *isn't* on the GCD. You're the shaman, though. You'll know which is right.