Establishing key performance indicators (KPIs) during the planning phase of an influencer marketing campaign is crucial to measure its success or effectiveness.

1. Define The Campaign Objectives: The first step is to define clear and concrete objectives for the campaign, which could range from boosting brand awareness, driving website traffic, generating leads or sales, or improving brand reputation.

2. Align KPIs With Objectives: The next step is linking KPIs with these objectives. For instance, if the objective is to boost brand awareness, KPIs could be reach, impressions, likes, shares, comments, or new followers. If the goal is to generate sales, conversions would be a relevant KPI to track.

3. Benchmark Against Industry Standards: You can also benchmark these KPIs against industry standards or previous campaigns. For instance, understand what a good engagement rate or conversion rate is for your sector.

4. Choose Right Platform: The choice of the influencer marketing platform also plays a key role. Some platforms like Flinque, offer robust analytics and tracking capabilities that can help you measure these KPIs accurately.

5. Monitor and Adjust: Lastly, always monitor the performance of the campaign and adjust KPIs accordingly. If a KPI consistently fails to deliver, it might not be the right measure of success for your campaign.

While these principles apply broadly, the exact approach would depend on the specific needs of your brand, campaign, and target audience. Different influencer marketing platforms may offer different analytics and tracking features that influence how you’ll monitor your KPIs in practice.