These are some of the block strings I use both mid-screen and in the corner
For reference [x] means hold and ]x[ means release
2A, 2B, 5B, 2C, 5C, [4]6A/B
You'll want to start to hold back as you press 2A so it's technically 1A, 1B, 4B, 1C, 4C
This is pretty decent as the A Orb will allow you to reset pressure or back away depending on the situation.
The B orb will keep you safe after the pressure at the cost of outright ending it.
Depending on the character you're fighting you'll want to do [4]6B over [4]6A.
For example at some ranges Gord can use 3C to slide under the orb and get a combo.
The characters I know you should use the B version on are Gord, Eltnum and Byakuya. (I don't get to play other characters very often so that's all I know)
If you find that you hit from 2A, 2B or 5B you can then do: (2A, 2B, 5B,) 2C, 5C, j, jC, [8]2A, 2C, 2]B[ for an easy combo and the option to restart pressure by popping the gem.
If you hit them with 2C a lot more options are open to you depending on how confident you are.
Some examples:
2C, 5C, J, JC, [8]2A, 2C, 2]B[ (Easy)
2C, 5C, JA, J, [8]2A, 2[C], 2]B[, 2A, 2B, 2]C[, J, JC, [8]2A, 2]B[ (Medium)
2C, 5C, JA, J, [8]2A, 2[C], 2]B[, 2A, 2B, 2]C[, 2B, [2]8B/C (Medium)
2C, 5C, JA, J, [8]2A, 2[C], 2]B[, 2A, [6]4A, 2]C[, J, JC, [8]2A, 2]B[ (Harder)
2C, 5C, JA, J, [8]2A, 2[C], 2]B[, 2A, [6]4A, 2]C[, 2B, [2[8B/C (Harder)
If you're in the corner you can also do these two additional combos
2C, 5C, JA, J, [8]2A, 2[C], 2]B[, 2A, 2B, 2]C[, jump and hold up and as you touch the floor either 2C, [8]2B or grab.
This set up is nice as it doesn't allow your opponent to punish [8]2B if it's blocked.
2C, 5C, JA, J, [8]2A, 2[C], 2]B[, 2[A], 2, 2]C[(as the gem is leaving re-hold C), back dash, 2]A[
This setup allows you to do Gem pressure which can be quite nice if the opponent doesn't know how to react to it
Gem pressure is done like so: 2]A[, 5A, 2]B[(as the gem is leaving re-hold B), 5A, 2]C[(as the gem is leaving re-hold C), 5A, 2]B[ repeat as needed.
The other Pressure I use is
2A, 2A, 2[A], 2B, 5C, 2C, 2]A[
You can then pop the gem with 5A or 2B and it will beat a lot of 2A/5A mashes. If they continue to block your options are:
Continue to pressure, use rising 9A to pop the gem and then a falling 9A to hit the opponent after which you can choose to do a [8]2B for a overhead or 2C for a low, run up grab (Not too often) or back dash away. There are other options as well so you can experiment and find more.
This set up outright beats Gord's 3C if you pop the gem but loses to Bayakuya's 2B and I think Eltnum's 2C beats it as well. (Probably other characters can beat it but I don't know which :P)
Against characters that can hit you as you pop the gem it's best to pause for a moment while crouch blocking to see if they do anything before using 5A/2B to set off the gem.
Honestly I don't know if these block strings are actually good or not. They're just what I've been using.
Also sorry for any inaccuracies.