Answer:
Don't be timid, don't be shy, don't be self-conscious. You can do a funny French accent, right? You can go 'Ah, monsieur, ze snails, zey are delicioos are zey not?' OK. Feel the way your mouth is when you do that, and keep it that way when you speak French. The secret of any accent is the mouth shape. Once you've got it, you're in business.
A little note on some vowels. The 'u' sound in French doesn't occur in English. You have to round your lips to make 'ooooo', and keep them there while you say 'eeee'. Practise this alone in front of a mirror. The nasal vowels are not all they appear; 'an' is 'ah' said through your nose; 'in' is 'eh' said through your nose; and 'on' is 'o' (as in hot), again said through your nose. get the sound by holding your nose, and you'll understand.