此外: besides, in addition
【四20】连词 / conjunctions
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
此外 (“besides, in addition”) opens a sentence or clause that adds one more point on the same subject: 我们要认真听讲，此外还要多做练习. A comma follows it, and the next clause often has 还 or 也.
It adds in the same direction and never contrasts (to contrast, use 但是). Its register is neutral to formal: emails, instructions, complaints, talks. In casual speech people say 另外. 而且 links two items inside one sentence and goes a step further, whereas 此外 moves on to a new point.
Compare 除了……以外，还……, which announces the list from the start: 此外 comes after the first point has been stated in full. So it always needs something before it.
Examples
这家店的咖啡很好喝。此外，价格也不贵。
Zhè jiā diàn de kāfēi hěn hǎohē. Cǐwài, jiàgé yě bú guì.The coffee in this shop is very good. Besides, the prices aren't high either.
这件衣服颜色不好看。此外，价格也太贵了。
Zhè jiàn yīfu yánsè bù hǎokàn. Cǐwài, jiàgé yě tài guì le.The colour of this piece of clothing isn't nice. Besides, it's far too expensive.
上课时要认真听讲，此外还要多做练习。
Shàng kè shí yào rènzhēn tīngjiǎng, cǐwài hái yào duō zuò liànxí.In class you must listen carefully; in addition, you must do plenty of exercises.
出发前请带好护照。此外，别忘了带一些现金。
Chūfā qián qǐng dài hǎo hùzhào. Cǐwài, bié wàng le dài yìxiē xiànjīn.Please bring your passport before you leave. Also, don't forget to take some cash.
这次旅行我们去了西安和成都，此外，我们还去了黄山。
Zhè cì lǚxíng wǒmen qù le Xīān hé Chéngdū, cǐwài, wǒmen hái qù le Huángshān.On this trip we went to Xi'an and Chengdu; besides, we also went to Huangshan.
公司的产品质量很好，价格也合理。此外，他们的服务也让客户很满意。
Gōngsī de chǎnpǐn zhìliàng hěn hǎo, jiàgé yě hélǐ. Cǐwài, tāmen de fúwù yě ràng kèhù hěn mǎnyì.The company's products are of good quality and reasonably priced. In addition, its service leaves customers very satisfied.
Common mistakes
✗ 我喜欢苹果，此外香蕉 → ✓ 我喜欢苹果，此外，我还喜欢香蕉 (此外 opens a full clause, it does not link two nouns).
✗ 他很聪明。此外，他很懒。 → ✓ 他很聪明，但是很懒。 (此外 adds in the same direction, it never contrasts).
✗ 此外，我昨天去了商店。 → 此外 leans on a sentence before it: at the very start of a text it has nothing to add to.