Maintaining a dwarf globe blue spruce's full, compact form through pruning requires planning.   You should be slow in your deliberation between cuts, and deliberate when you make cuts.

Some ground rules:

- Blue spruce does not produce buds on stems that lack needles.  It's sometimes called "dead wood," but the wood isn't dead; it'll just look like a stick because it won't produce buds and then new growth.  If you need to prune back to "dead wood," you should remove the whole branch back to the main stem.

- None of what you read or were told about timing was wrong.  The buds on the stems with needles formed last year.  So, you could prune right now.  However, waiting until later this spring when the new growth (candles) has elongated but it's still pliable means you'll get more buds forming that were stimulated by pruning cuts.  This will give you denser foliage.  To maximize the effect, cut away about half the length of the candles.  Of course, step back to see how the prolific new growth affects the tree's shape.  Confine your cuts towards the top if you want a tree a bit wider at the top, or make your cuts at the bottom if you want a fatter tree.

- If you need to do more dramatic pruning, you can cut back to where other lateral branches are growing from branch you're cutting.  But this is where slow deliberation pays off.  These more drastic cuts can create holes.  And although they will eventually fill in, the effect can be unsightly on a globe if you don't make the cuts so they're somewhat hidden.

Thanks for sending the picture because it provides another consideration.  Have you considered moving it?  Digging it out and transplanting it, perhaps just a few more feet away from the sidewalk, would be your best long-term solution.

It looks like the main concern is the spruce growing into the sidewalk.  However, it will be impossible to keep the spruce away from the sidewalk without eventually producing a flat-sided, mishappen tree.  It looks like that's already starting to happen.

The value of dwarf globe blue spruce as well as many other dwarf conifer cultivars is that they shouldn't need pruning to retain their nice, compact shape.  However, they should be positioned to allow them to fully flourish.  Even though it's a dwarf, we always recommend using the eventual width to guide positioning it in the landscape.