Have you tried to operate in Asia? Just try to keep the missions random and avoid a pattern your opponent could exploit. How long until we hit plasma rifles and floaters/snakemen? And grenades, don't forget grenades.
I went to Asia once. I immediately got shot down, IIRC. I think hes got his base around there, so I tend to avoid it.
Its not that my missions aren't random, its just that after a few waves he'll have his ship planted right at my base and detect one of said ships, follow the direction, send all his ships to that region...you get the idea.
I've always had grenades. I just need to fully equip my ships. At low, no one gets grenades. Medium, 1/2 of soldiers get grenades. At High, Grenades for Everyone!
Plasma rifles are almost done. Unfortunately, all I have is one medium scout. If I can squeeze like 2-3 good abduction missions out of it, plasma rifles will finish
After plasma rifles, I'll likely upgrade ship tech, so I'm not just flying medium scouts around. After that I'll work on racial tech. So probably Plasma Rifles ---> Large Scout - ----> Floater ---> Abductor ---> Snakeman. Unfortunately, large ships can not be operated by Sectoids until you have psionics, because Sectoid leaders have mind control. So I have to research Floaters before Abductors.
Last thing that I forgot to mention in any updates. Each race has a specialty in missions, and give like a 2x increased benefit to the mission(or something like that). Sectoids are good at abductions, floaters terror, and Snakemen harvest. I usually don't like going race first because terror missions are useless until March, so the only benefit of having floaters is that they...float. They can't even throw grenades, at least I'm pretty sure.