Summarize:

While the French language has a lot of accent and diacritical marks (the marks over letters) that can trip up beginners, none of these marks are present in French numbers. Getting down the basic vowel sounds and practicing them with numbers can help improve your overall French pronunciation. A is pronounced like the a in the English word "father." The combination ai is pronounced like the ai in "bait," and au like "oh." An e without any accent marks is pronounced like the oo in the English word "good," as is the combination eu. When coming before an f, it sounds more like ur, as in neuf (9). I is pronounced like the ee in "see." You notice this in the number words six and dix. O is pronounced like "oh." The combination ou sounds like the same vowel combination in the English word "soup." U may be pronounced similar to the oo in the English word "food," although the exact sound doesn't exist in English. Since you won't find this u sound in number words, feel free to skip it for now. Anytime a vowel is followed by an n, it is a nasal vowel. This will alter your basic pronunciation. For example, in the word un (1), the u sounds more like eh or uh. French uses essentially the same alphabet as English, and most of the consonants are pronounced similarly. The ones that are pronounced differently are fairly easy to remember once you've had some practice. When the letter h appears at the beginning of a word, it's usually silent. For example, with the word huit (8), the w sound comes from the pronunciation of the vowel combination ui. The h at the beginning is silent. Whenever you see a q or qu in French, it is pronounced like an English k. You can see this in the number words quatre (4) and quatorze (14). This pronunciation is found occasionally in English words, such as etiquette, which are loanwords from French. The letter c is pronounced like an English s if it comes before an e or an i. This isn't really different from English, which also has a soft c, as in the words "office" and "face." In fact, most of the English words with soft c came from French. The French r sounds quite a bit different than the English r. This is because the sound comes from the back of your throat, rather than the front of your mouth. The French r is guttural, but not as guttural as some sounds in other languages, such as German. Think in terms of the sound you would make when you were gargling, but not the sound you would make if you were clearing your throat. To find the correct place to make the French r sound, make a k sound with your mouth closed. You should feel it at the base of your tongue. Practice making an r sound from that spot. It can take some time to get it right, but until you do, take comfort knowing that you will still be understood if you use a regular English r or a slightly trilled r sound. Nasal sounds figure prominently in many French number words, including vingt (20) and un (1). To make the nasal sound correctly, cut off air flow in your mouth and send part of your exhalation through your nose instead. Generally speaking, if you see an ng in a word, it is a signal to pronounce the vowel nasally. Many English words with an ng, such as sang, are also said with a slight (or significant, depending on your regional accent) nasal twang. You may be familiar with the silent e in English, but French also has many silent consonants. Some of these lettres muettes (silent letters) appear regularly in French number words. For example, in the word vingt (20), the g and t are essentially silent (although the ng signals that this word should be pronounced nasally). The word quatre (4) is another French number word with silent letters here, the r and the e are both silent.
Start with the French vowels. Pronounce most French consonants as you would in English. Say the French r from the back of your throat. Practice the nasal sounds until you get them right. Leave off the last letter when pronouncing many French words.