How do i get better in mvc3?

To start this off i got this on launch day. I played it alot. My favorite characters would have to be Chris Redfield and Dante. Whenever i play online i always get beaten up badly. Sentinels were a huge problem for me but since the patch they dissapeared. I did all of Dante's and Chris's trials all 10. It took me a long time and i cant actually link them into anyone. I bought the fightpad it was the last one anywhere in my city. it takes a little getting used to. when i play i cant do the combos i do in training mode. I dont know if its lag or what. Characters like chris become really slower online and become useless in front of fast characters like X-23, Wolvie, and etc. Help what do i do to cope with that.