If you're looking to add some ASX dividend shares to your portfolio, then you might want to consider the three listed below.
Both of these ASX dividend shares offer decent yields and trade at attractive levels. Here's why I would buy them in September:

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Accent Group Ltd (ASX: AX1)
I think this footwear-focused retailer could be a dividend share to buy. Accent owns retail store brands such as Athlete's Foot, HYPE DC, and Platypus. Pleasingly, demand for footwear has remained strong during the pandemic, leading to Accent delivering a full year result to be proud of in FY 2020. It posted a net profit after tax of $58 million, up 7.5% year on year. Pleasingly, given its expansion plans, strong online business, and its on trend offering, I'm confident Accent will continue its positive form over the coming years. In FY 2021 I expect the company to pay a 9 cents per share fully franked dividend. Based on the current Accent share price, this means investors would receive a 5.8% dividend yield.
Dicker Data Ltd (ASX: DDR)
Another ASX dividend share to consider buying is Dicker Data. It is a wholesale distributor of computer hardware, software, and cloud solutions exclusively to a partner base of over 5,500 resellers. Dicker Data distributes a wide portfolio of products from the world's leading technology vendors. This includes Cisco, Citrix, Dell Technologies, Hewlett Packard Enterprise, HP, Lenovo, Microsoft, and other Tier 1 global brands. Demand has been strong for its offering in recent years and underpinned consistently solid earnings and dividend growth. This has remained the case in FY 2020, leading to management guiding to a 31% increase in its dividend this year. This will bring it to 35.5 cents per share. Based on the current Dicker Data share price, this equates to a fully franked 4.75% yield.