Checkout is the last hurdle before the customer becomes a customer. And it's where most lose them. 69 percent of all carts are abandoned according to the Baymard Institute. A large part is due to the checkout experience.
Fewer fields
The default WooCommerce checkout has fields for first name, last name, company, address 1, address 2, city, postcode, country, phone, email, and then optionally shipping address (same fields again). That's too much. Remove the company field if you sell B2C. Remove address line 2 if it's rarely used. Every field you remove increases conversions.
Checkout Field Editor (free plugin) or Flexible Checkout Fields. Hide, remove, or reorder fields without writing code.
One-page checkout
Default WooCommerce checkout reloads the page at each step. WooCommerce Blocks (built in since WooCommerce 8.3) provides a modern checkout built on Gutenberg blocks. Faster, better-looking, better mobile experience.
Express checkout
Apple Pay, Google Pay, and Klarna Express Checkout let the customer pay with one click (or fingerprint). The address is pulled from the payment method. The customer doesn't need to fill in anything. Stripe Payment Request Button or Klarna Express enables it.
Guest checkout
Don't force customers to create accounts. Under WooCommerce → Settings → Accounts: enable guest checkout. Offer account registration as optional ("Create an account for easier shopping next time"), not as a requirement.
Trust signals
Show SSL padlock, payment icons (Visa, Mastercard, Klarna), return policy, and customer service contact info at checkout. Customers who feel uncertain abort. Trust signals reduce uncertainty.