Do basic math.
Ok, so to elaborate, instead of picking fights or positioning units based on “vibes”, make plays assuming the worst outcomes (in regards to your units getting hit and missing counters especially).
The math is rarely that complex; if my unit has 16 current hp, and the 3 enemies in range all do 5 or less damage and do not double, the play is relatively safe; they will survive. If each of those enemies do 7 damage instead, seriously consider the risks of unit death or any alternative strategies, even if all the enemies are rocking lower hit percentages.
Also, if you are going to take risky odds, perform them as eary on in the player phase as possible, and be ready to use player tools to accomidate the failure (rescue, shove, staff usage, and so on).
In my experience with FE, both official and fan made, you rarely have 0 safe moves. Learning what moves are safe, and how to make moves safe, is a key skill to develop for getting good at tactical and strategic games in general, not just FE.
Finally, a fun annecdote, but my development of these strategies was motivated primarily by my consistently horrible luck; in any game where dice or RNs are rolled; I predictably encounter the worst results. But I can still enjoy many FE games, because with good strategy, it takes an astronomical streak of bad luck to make a map unwinnable.
Sorry for any spelling or grammar mistakes, hope this helps.