Coffee first thing, before you've eaten anything — a lot of people do it, and a lot of people also feel jittery or a bit off afterward.
Caffeine on an empty stomach gets absorbed faster, since there's no food slowing things down. For some people that's fine. For others, it means a sharper jittery feeling, or stomach discomfort, because there's nothing buffering it.
Having something small first — even just a piece of toast — tends to soften that. Splitting your caffeine into smaller amounts rather than one large coffee can also help, since there's less hitting your system in one hit.
Some people use Neuchu for exactly this — a smaller, fixed 50mg dose instead of a full coffee straight off the back of nothing. You can find it here.