From the 70's, I don't know many authors yet.
From the 80's, good starting points would be "The Belgariad" and "The Malloreon" by David Eddings. You could also read "The Elenium" and "The Tamuli", also by Eddings, but you would recognize a lot of concepts from the other two works. Some things are are actually *VERY* similar.
If you're reading Eddings, skip "The Dreamers." Seriously. It's a four book series, but it's basically half the characters (with matching traits) of "The Elenium". Book 1 is OK-ish (but just), with Book 2 you're thinking: "Didn't I just read that in Book 1... in a different part of the same world?" and by Book 3 you're ready to shoot yourself. Or worse. It's the only series I actually abandoned and didn't buy in ebook format.
I hear "The Dreamers" is now used as torture material in prisons around the world by broadcasting the audiobook version over the prison's intercom speakers.
A very good book is "The Elfstones of Shannara" from 1982 by Terry Brooks. While it's not the first book in the trilogy, it's a better, more original book that its predecessor "The Sword of Shananra" from 1977. Of "Sword", it's said that it's a rip-off of Tolkien. While I wouldn't go THAT far, the similarities are unmistakable. "Elfstones" is a book that can stand on its own. It's actually my favorite book, despite the fact that the title is wrong (the plot is NOT about the Elfstones... those are just a plot device), and that it has at least two very annoying characters. The best part of this book is the ending. It's a plot twist you'll probably remember for the rest of your life.
If you like shared worlds, you can look into R.A. Salvatore's first six Drizzt books, from the late 80's and the early 90's:
1. The Crystal Shard
2. Streams of Silver
3. The halfling's gem
4. Homeland
5. Exile
6. Sojourn
Book 4-6 are a prelude to book 1-3. Many people nowadays read the trilogies the other way around: 4-5-6, 1-2-3, so they're in chronological order. At this time, that is also the official series order of
"The Legend of Drizzt"
Two series on my "soon to read list" are The Chronicles of Thomas Covenant (starting in 1977, with "Lord Foul's Bane"), and the "Darwath" series by Barbara Hambly, starting in 1982 with "The Time of Dark." I haven't read those yet.
From the 70's, I only read Mary Stewart's The Arthurian Saga, which is a fantasy series based on the legend of King Arthur. I read them a long time ago, in paper, in Dutch, from the library. I don't even know if they are still in print and if there are official ebooks of this series.