Just to be clear about the terminology, I've drawn up an image:


The strategy is to work one layer at a time. Layers do not affect each other.

Count how many nodes are on each side of the given layer. Say you have 5 on the left and 5 on the right (5,5) for layer 1, (3,2) for layer 2, and (1,4) for layer 3. You'll want to take the max(a,b) for each layer. In this case, 5, 3, and 4 for layers 1-3. This is the amount of blocks you have to put down for that layer. So for layer 1, you have to put down 5 blocks such that it lights up all of the hints for that layer, layer 2, spread 3 across 2, and so on.

A good thing to note is that to satisfy one hint with N blocks, you build adjacently, and to satisfy M hints with N blocks, you build diagonally. So you can figure that for a (4,2) layer, you'll have two diagonal sets of two adjacent blocks.

If done correctly, you'll get the minimization expert requirement for that level. If not, clear the board and be a little more careful, paying attention to the number of blocks placed per layer and whether or not you're accidentally placing blocks in the wrong place/layer.

Here are some visuals to help out, using what I consider to be one of the harder levels.

Same as minimization, but instead of max(a,b), you're taking a*b.

This is so easy it can actually be brute-forced. If you make a column in the corner, build a wall for each layer, and extrude it out into the layer, deleting rows where the hints are showing X's, you're guaranteed to get it. But knowing what to expect for each layer helps, too.

Again, visuals

The picross levels are easy. Also, it's not picross. If it were, [2] would actually mean [2] and not [1 1].

That said, it can be tricky to "see" where the rows line up, so as long as you're careful, and go for the big numbers first, you should get it relatively quickly. Solving layer-by-layer works here, too. So don't move on to the second layer until you've completely solved the first, and so on. The reason is because, of course, building too high will block your view of lower layers.