A lot has been said already, and it's all great advice. I'd just like to add a few things. First, you definitely need to block more. Tager has the highest health in the game for a reason: he was designed to be beat up. You can take more hits than any other character in the game, so don't be afraid if you fail to read a high/low mixup. Also, take into account the character you're playing against. A character like Ragna or Makoto needs to get close to deal real damage to you, so in that situation you might consider waiting for them to approach, and punish them for doing it. If Makoto is turtling, spaming projectiles, then sit and block them, or voltic charge. Having more health gives you the right to turtle and waste the clock, a viable strategy against those afraid to approach Tager. This will force them to move in. Zoning characters like Lambda and Rachel will require you to move in, however your sledge will be more effective than against non-zoners like Makoto.
Throw out spark bolt. It's debatably the best projectile in the game; it comes out of nowhere, hits full screen, is extremely difficult to punish, magnetizes even on block, and absorbs other projectiles. Too bad you don't get a lot of them. So watch that little yellow meter at the bottom of the screen. Try not to be to predictable with it.
And bursting out of an opponents larger combos is a great tool, especially for Tager whose large primer count makes up for it.