start with anti-airs. I'll bet opponents are able to jump in at will against you, so have that in mind and be ready to hit them with a crouching hard punch.

after you get that timing down, move to doing a medium dragon punch against jump-ins. it does 50 more damage and covers more options. if you can't reliable hit a DP, then practice that for awhile in training.

avoid sweeps because they're mostly unsafe in this game. avoid jumping in like crazy yourself, and mix in neutral jumps (straight up jump). avoid pressing attack buttons that are not in range to hit. when you get knocked down, it's ok to block. practice walking forward and blocking. always mix-in a throw.

the cool part about SFV is that the people beating you know more about the game than you do, or can just out-execute you on a consistent level. I can anti-air most everyone ranked below my level, but the people ranked above me time their jumps better and space them better -- so I get hit by *their* jump-ins with the same characters. fair is fair.

I put about 400 hours into SFIV and could barely beat the CPU on medium hard when I started. but I got to a level where I had a lot of fun playing similarly ranked opponents online.

in SFV, I feel like I'm getting better faster because the game breaks your bad habits quicker. I know I'll never be great because my execution and reactions are not the best (hit confirms, argh). but I have fun playing, and try to keep learning more about the game every time.