It sounds like the reason why you’re not doing so well in SF4, is because ALL you’re trying to do is land combos. Combos are, in my opinion, the least important aspect of SF play. You don’t get KOd because you dropped a combo, you got KOd because you took WAY too much damage, put yourself into many bad situations, and played recklessly.
If you want to do better, I suggest you stop worrying so much about doing trial mode combos and advanced links, stick to basic bnb combos that you can reliably, and during a live match. Spend the rest of your effort worrying about your defense, your spacing, your ability to block mix-ups, cross-ups, throws, as well as your ability to anti-air jump ins. Offense isn’t what wins you the game, it’s defense.
As far as landing links go, other than the plinking method and double tap execution tricks, you’re going to have to practice. No shortcut for that, just daily practice in order to get it locked into your muscle memory, so that when you actually bring those combos out to a real match, you’re able to do it effortlessly.
And read the execution stickies in the newbie section.