SEM or Search Engine Marketing generally means paid advertising. The opposite of SEO, Search Engine Optimization, which focuses on website traffic from organic, or non-paid sources. Inbound marketing is traditionally a focus on organic website traffic, but even the Inbound leaders like Hubspot acknowledge the place SEM has in online marketing. For it to be low hanging fruit it must be cost-effective, targeted and result in a quantifiable return on investment. 
There are specific targeted campaigns you can launch to get the “low hanging fruit”:
- Remarketing to previous website visitors.
- Targeting your best customers.
- Targeting people like your best customers.
Outside of campaign targets there are also measures you can take to pick the “low hanging fruit”:
- Bid adjustments based on time of day, the day of the week and the competitive environment.
- Using machine learning to optimize bidding and budgets.
- Leveraging best practices. Examples for Google Adwords include Dynamic Number Insertion to track leads and conversions at the keyword level.
