Cost per Click(CPC) is the best way to start with for beginners, ads are usually banners, text or videos that you place in your content or sidebar. Each time a reader clicks on the ad, you are paid for that click. Adsense is the most used cpc ad network.
Sell ad space
If you are getting enough traffic you can sell sponsorship ad space on your blog, you can contact the advertisers to pleace thier ads on your blogs, few times advertisers may contact you directly to ask you to place their ad on your site.
Affiliate marketing is the most effective way to earn more money. You can find right product or service related to your niche and start wiritng a review of the product or place banners. Remember you will only get paid when you make sale.
Offer sponsored post service on your blog, Charge for posting review of a service or product, there are many advertisers who is will to pay.
You can also consider selling you own digital products/service like ebook, Online courses, workshops and etc. You can also setup a membership site too.
If you find any other way to monetize a wordpress blog share it with us using below comment section.