If done right, upsells can be an effective way to increase your total order revenues. The key here is making sure it is on the right page at the right time— and noticeable.
By default, upsells on WooCommerce show up on single product pages below all the content. Cross-sells show up on the cart page, again specifically below the list of items in your cart.
There are several plugins and extensions that will help you strategically place an upsell. Frequently it’s an added feature that does a lot more than that.
But if you are looking for something simpler, say an extension that adds an upsell on the cart page only and places it a bit more front and center, you might want to check this one out.
The Cart Upsell for WooCommerce Extension
To set this up, just go to the product you want to offer as an upsell. You will find an option to toggle it on and so it appears in your product data.

Now you can set up the display and rules for the upsell. First there are a few options to customize it with a message, picture and color for both the banner and add-to-cart button.

Next you will add condition with an and rule group or a or rule group. You can control where it appears down to the finest detail. These can be set by product, category or cart total.

For example, a simple condition will be based on a single product. I have a mic boom arm and am upselling it with the purchase of a microphone.

If the customer adds the mic to their cart, they will now get this message and can simply click on the add-to-cart button without leaving the page.

Another scenario could be based on cart total. For example, I have created a product, a podcasting video series that fits with all my products. I have hidden it from my search and shop page because I want to offer it as an upsell at a big savings. But I want to make sure they spend enough to make it work on my end as well.
I have set the cart total for the amount as a rule. And since it makes sense to sell with specific categories, I have chosen three of those. In addition, since the upsell is not in the product categories I have selected, I can be rest assured that they won’t be sold the video series as an upsell even if they were purchasing the videos. Otherwise, I would have wanted to set another rule excluding the video series.

And as you can see, if all conditions were met, including the cart total of more than $300, the upsell appears.

To set this up, just go to the product you want to offer as an upsell. You will find an option to toggle it on so it appears in your product data.
If you are looking for a simple solution to add upsells to your cart page, I suggest you check out the Cart Upsell for WooCommerce extension.