@Aldarion Interesting topic. I'll toss in my two cents....
I believe Tolkien took great pride in presenting the big picture. His vision for Middle-earth was grand. He sought to present major themes regarding culture, government, and theology and then delve only into specifics in certain areas. For example, Tolkien presented us with the major themes of friendship, family, and language... and in the area of language he gave details (hundreds of words and working alphabets) on the workings of Quenya, Sindarin, and Adunaic.... while only teasing us regarding Hobbit-ish (Hobbit-ese... if there is a real name, it has escaped me), Khuzdul, The Black Tongue, and Rohirr -ish (Is that a word?). He gave us no information on the wedding and funeral rites of the Shire, but gave us more than enough information on birthdays.
Obviously, he was greatly intrigued by alphabets, calendars, birthdays, and songs/poetry.
In the area of government, he did not go into great detail... but he was very concerned with justice. I think his opinion was that the only reason for war is to establish justice and peace for the people. Overall strategy was necessary to discuss, but he really enjoyed presenting individuals fighting to do justice. Sam vs Shelob. Theoden's charge. Gandalf vs the Balrog. Beregond vs Denethor's servants. I can't find my books, but doesn't Aragorn say something to Eowyn like, "Your place is here. If we fall, you will still have to fight. That fight will be no less honorable though there will be none left to sing of it." I think that shows that Tolkien does not really care about the tactics... and that the strategy is included because it has to be... but what is of vital importance is that the effort is made. Boromir's defence of Merry and Pippin is not descibed... only it's aftermath... but the attempt was undertaken, the sacrifice was made is not any less for failing.
I say all that to merely agree with the comments of Overread and Aldarion.
@Foxbat I semi-agree. Sauron's strategy was to avoid the shanking by the Last Alliance, as Aldarion mentioned. But I'm not sure that he always felt comfortable in using the human wave as a tactic... as a strategy, yes. Aldarion and Overread mentioned above that Sauron's strategy was long term. The build up to the War of the Ring was three thousand years in the making. The realms of the Noldor, the Numenoreans, and their various allies needed to be dealt with piece meal.
The Witch-king accomplished the destruction of half of the Numenorean realms. A balrog and dragons dispersed and lessened the power of Durin's descendants and Laketown. Sauron himself befouled southern Greenwood drove Thranduil's folk north. A long series of raids and invasions by Easterlings and Southrons gradually wore down Gondor. And the Noldor of Ered Luin gradually grew weary and withdrew physically to Aman or emotionally by isolating themselves from Rivendell and Lothlorien.
Speaking in broad terms, Sauron had greatly weakened the Free Peoples since the Last Alliance while greatly growing in strength of numbers and geography. Yes, Gondor had acquired two new allies in Rohan and Isengard, but Sauron had secretly turned Saruman to directly oppose Rohan.
Didn't Gandalf say something about Saruman to the effect of... "...I perceive only a finger of Mordor"...?
Anyway, regarding battle tactics I don't know that Sauron used waves. It can be presumed that the Uruk-hai employed this to bring down mighty Boromir and to try to break out of Eomer's trap. I can't say he did not either because the commander of the assault on Minas Tirith was the Witch-king... and the chief weapon of the Nazgul was terror... to their enemies... and probably to their own troops as well. I do agree that Sauron had little to no regard for any of his troops. The appendices say that Sauron lauched three distinct assaults from Dol Guldur to Lothlorien.
Also, Aragorn was concerned about Sam's wound in Moria because orcs sometimes poisoned their blades. Poison usually takes longer to act than a battle so why poison if your troops are attacking in banzai charges?
Even if his five assaults (Easterlings againstDale and Erebor, Dol Guldur against Lothlorien, Dol Guldur against the Elves of Mirkwood, (a defensive army to separate Rohan and Gondor), the Witch-king against Minas Tirith, and the Corsairs against southern Gondor ) failed (which they did), Sauron's plan was that he could breed and recruit new armies faster than Elves, Dwarves and Numenoreans. That was always his plan.
So.... strategically steam roll his enemies, yes... tactically use human waves, maybe.
So one tactic I have not seen mentioned is night fighting. Orcs did not like the sun, trolls could not endure it, and even wargs seem to prefer the night. The fellowship was attacked at night by wargs. Aragorn, Legolas, and Gimli were confused when the orcs traveled through Rohan by day. Sauron's blotting out of the sun allowed his legions of orcs to be bolder and for his trolls to be used as beasts of burden at Minas Tirith.
Outnumbering the opponent usually means your line can overlap and envelop his. I assume Sauron liked this. Presumably this is what happened at the ambush at Gladden Fields.