Additionally, regarding the use of training mode:
When frame data is not available, or you think you just need a visual indication of how +/- on hit/block something is, go into training mode in a mirror match and record the dummy to use whatever move you want to check out then hold up. Going back to controlling your character, let the dummy connect with their attack on hit/block then hold up. Whichever character jumps first has frame advantage (they jumped first, meaning they could have taken any other action first), the difference in height will give you an idea of how much. Some games have a 1-Guard Jump setting which makes this easier to check for advantage on block.
When practicing combos, make sure you also learn to reliably confirm into them. You don't want to go from your pressure to committing to an unsafe move without making sure it will connect, and relying on cancelling everytime into a safe special that would have also been your combo ender anyway will often kill your momentum and limit your general offense anyway.
Hit-confirm practice is what Random Guard is for. You generally need the ability to confirm off 2 light attacks. What you do is set the dummy to randomly block and input the 2-hit sequence, but only go into the rest of the combo if those 2 hits connected on hit. In a real match if you saw those 2 hits get blocked you'd want to go for something else like a throw, go back to blocking, another poke, general movement or whatever. The point is to recognize what actually happened when you went on offense and act accordingly.
If you're having execution issues, do turn on input display and look at it carefully. Look for any unnecessary or missing inputs. If everything is there but whatever you wanted didn't come out, you were most likely just too slow, but cleaning it all up is a proper first step before trying to do things faster, even if modern games tend to be more lenient with respect to that.
