It might be that your campaign is performing badly; either because your frequency is too high or too low. That's why we propose solutions for campaigns that aren't doing well because of the frequency.
Increasing your frequency
If the campaign goal is Reach, then follow these steps: open the campaign, select all ad sets, and then choose Edit selection. After that, pick Bid info in the drop-down menu. In Optimisation goal choose Daily unique reach. There you can select the Interval that will state how many times a day your ad will be seen by each person. Afterwards select Impressions in Billing event.
Another option can be optimising for Impressions. You can do this by editing a selected ad set, then select Impressions in Optimisation goal. By this way the campaign's impressions will boost automatically, no matter what the campaign goal is.
3. The last option is to put your campaign on accelerated delivery, which will increase the odds of your ads being shown to a larger amount of people.
Decreasing your frequency
When your frequency is too high, it means that the relationship between your audience size and ad set budget is not adequately set up.
To establish a proper relationship between what you spend and who you target, firstly you need to know what type of campaign you are running.
If it's a conversion or prospection campaign, the solution is simple: just broaden your source audience—that is, target more people. You can add more interests, more locations, or even more languages.
If it's a retargeting campaign, you can reallocate the ad set budget you are spending on this campaign in the prospection campaign.
There are many ways to control your frequency. The first one is by having a Reach campaign. In this way you can state how many times you want your audience to see your ads. To do this, open the campaign, select all ad sets, and then choose Edit selection. After that, pick Bid info in the drop-down menu. In Optimisation goal choose Daily unique reach. There you can select the Interval that will state how many times a day your ad will be seen by each person. Afterwards select Impressions in Billing event.
The second option is setting automated rules (when frequency is x, pause the campaign). You can read more about them in this article.
Reach and frequency buying is another option, but it's not very advisable. Bear in mind that running a R&F campaign can lock in your potential, as your campaign is conditioned by the limitations you've set.
Finally, you can monitor your campaign closely (as mentioned above). You can expand the target, add new creatives, or simply pause ads, ad sets, or campaigns if it seems your audiences may be getting fatigued based on high frequency.