I had a couple of bad experiences with Esbit cubes a few years ago. As you know, the surfaces of a cube are pretty smooth and solid, and that helps avoid the cube breaking up prematurely. That also makes it harder to light. So, if I think that I will have any difficulty lighting a cube, I use a knife to carve up the edges where I want to light it. That produces tiny surfaces that are easier to light, but it takes only a few seconds to prepare. The extreme case would be using the knife to chop the whole cube up, but I've never had to go that far.
I found a lot of difference between real Esbit cubes and off-brand cubes.
The other thing is the lighter. I admit to using a mini-bic currently. However, if the weather is colder or I suspect that I could have lighting difficulty, I carry an oversized standard butane lighter that has an adjustable flame control. Then, assuming that I store the lighter in my pocket to keep it warm, I can get a good flame out of it, and that helps light the Esbit.