The goal is to find keywords that people are most searching for in Google, relevant to your content, and with the highest chances to rank for.
By priority, the first filter to select keywords is competition. Focus on keywords with low competition and with traffic volume of at least 10-100 searches per month.
Most keywords with two or fewer words usually are hard to rank for, as they're used broadly in different contexts.
For example, let's look at "sales management".
Because sales management is a broad topic and included within many types of search queries, this is a keyword that has high traffic but difficult to rank for.
But there are some keyword exceptions as you can see in the screenshot below.
Both of these keywords, while fewer than three words, have low competition and monthly traffic. While ideally you should always be looking for keywords with three or more words, in some cases, two words will do.
Here is another example "role of sales management". This is the type of keyword that I try to go for.
These tend to be more specific, three or more words, thus other than having better chances of ranking, they also usually tend to convert traffic better—more people clicking on your ranked content from the search results.
To recap, select target keywords with low competition and monthly traffic. Most keywords with two or fewer words are hard to rank for, but there are some exceptions. However you will always be better off if you can find keywords with three or more words. Not only they are usually easier to rank for, but they also tend to convert traffic better because they're a closer match to what the user is searching for.