Good anti-air is 6A.
Standard strings are a good way to keep pressure.
5A/2A, 5B/2B, 5C, any special -> followup
5B, 5C, 5D, delay 214A -> 214D
5A/2A, 5B/2B, 5C, 2C, 214A -> 214D
3 Combos you should learn as a basic tactic.
The BNB air combo which is a must know is:
j.C, j.D (JC), j.C, j.D, 623D -> 236C -> 214C
IS A MUST KNOW.
And then learn:
j.B, j.C (JC), j.C, j.D, 623D -> 236C -> 214C
Learn these and you'll understand how Ragna creates pressure. Experience and insight through how the combos work will give you the ability to create pressure with Ragna.
Also watch Kaqn on youtube. There isn't a couple of sentences or a flow chart for Ragna. He is not one of the top 3.