There are a few different options when labeling items, such as equations, tables or figures. Any of these are fine as long as the conform the style guidelines and are applied consistently throughout your document. For journal papers and conference papers, be sure to follow the approach used in the sample papers or the template provided by the publisher. It is really a matter of preference. Some possible approaches are below.

Approach 1 – label each group sequentially (most common)

Example: Table 1, Table 2, Figure 1, Equation 1, Equation 2, Equation 3, …
Advantage: It’s easy see how many of each item, such as how many Tables, there are in the whole paper.
Disadvantage: It’s not obvious where one component sits in relation to another type of component. For example, Table 2 might be at the end of the paper whereas Equation 5 could be in the middle of the paper.

Approach 2 – label each group sequentially within chapters (very common)

Example: Section 1: Equation 1.1, Equation 1.2; Section 2: Equation 2.1, Figure 2.1, Figure 2.2, …
Advantages: It’s easy to know which section to find an item in. For example, if the text references Equation 3.2, the reader knows to look in Section 3 to refer to it.
Disadvantages: It’s hard to see how many Figures or Tables are in the entire paper.

Approach 3 – label each item sequentially (not as common as Approach 1 or 2)

Example: Table 1, Figure 2, Table 3, Table 4, Figure 5, …
Example: Lemma 1, Lemma 2, Equation 3, Theorem 4, …
Advantages: It’s easy to find where you are in the paper as number 4 will always be between numbers 3 and 5.
This is sometimes used in mathematics-heavy papers to show the sequence of steps required to get to a key theorem.
Disadvantages: It’s hard to see how many Figures or Tables are in the entire paper.
Some people might feel like numbers are being skipped if they see Equation 3, 5 and 6.