Try to avoid speaking slowly and hesitantly, as this will distort the tone on the word and make you much more difficult to understand than if you spoke confidently. When speaking fairly quickly even the Thais routinely don't pronounce each and every tone, as there's simply not enough time to do so. If your tones aren't perfect, you stand a much chance of being understood by talking at the same normal speed, rather than hesitantly. You'll know you're well on the way to getting it right if you start being told that you poot tai chat (speak Thai clearly) rather than simply geng (well).