There is no 100% safe way to approach anybody 100% of the time, but there are options you can choose that are safer than others, depending on the situation or character you're fighting. In general, you don't want to do anything at neutral that they can react to, especially nothing like B/C/D ice car, air dashing or jumping at them. This is because they can see it in time to anti air you, or just block and punish whatever you're trying to do. Instead, at farthest ranges, it's a better idea to throw out a projectile first and run behind it (though this is a bad idea vs. certain characters like I said, see nu), throw out a 236D and do the same thing, or when you're not so full screen away (most often) just space with normals.
By "space" I mean you're creating an area of space that your opponent has to respect. Your neutral D (5D) does this pretty well, in conjunction with your uppercuts (A and B are better at spacing than outright anti air from my experience). Once your opponent understands that he needs to approach -you- more carefully, you can move in closer, at which point you do your block strings, high/low, hit/throw, whatever. If they "block forever", two things: you should probably work on your offense and, even if they are blocking all you do, there is a guard break in this game. You may not often actually get the break, but the threat of it and the mind game involved will coax them into taking more risks to get out, which you can punish/react to.
As for the other guy's question about punishing things, that depends on what they did and where you are. If you Barrier Guard btw, then you shouldn't be blocking stuff for too long. 6C is not something you punish with, it's not even a move you'll do outside of a combo unless in like, really rare occasions. Try a DP, wave super or a faster normal.