I would also suggest the captain marvel 25-33 storyline. Go buy some beaters to read.
Iron Man #55 starts you off of course.
Captain Marvel #25-33 is next. Marvel Feature #12 and Avengers #125 should be read too during this period.
This leads into Warlock #9-15. His Origin is in #10. This run cannot be missed. He does sit out 12 & 13 but if you're going to do it right you really should read the whole run. Warlock plays a HUGE part in all this and those issues give you a huge insight into the character.
And then you go to Avengers Annual #7 and Marvel Two-In-One Annual #2 for the end of what Jim Starlin refers to as the First Thanos Saga.
The Death of Captain Marvel should be read next. Take an intermission, have a beer and pizza and then come back.
Start anew with Silver Surfer #34-50 and then Infinity Gauntlet 1-6 for the 2nd Thanos Saga.