The thiocyanate ion, SCN⁻, has the atoms in the order S, C, N and 16 valence electrons.

Step 1. $\text{S=C=N}$. S: $6 - 4 - 2 = 0$. C: $4 - 0 - 4 = 0$. N: $5 - 4 - 2 = -1$. Sum of sizes: $1$.

Step 2. $\text{S-C}{\equiv}\text{N}$. S: $6 - 6 - 1 = -1$. C: $0$. N: $5 - 2 - 3 = 0$. Sum of sizes: $1$.

Step 3. $\text{S}{\equiv}\text{C-N}$. S: $6 - 2 - 3 = +1$. C: $0$. N: $5 - 6 - 1 = -2$. Sum of sizes: $3$.

Step 4. Choose. The first two tie. Nitrogen is more electronegative than sulfur, so $\text{S=C=N}$ is the best. In practice both of the first two contribute.