The checklist for onsite trips varies with the destination—meaning much of the content is country-specific, even though the general aspects like air tickets, visa processing, etc., would be, by and large, common. However, those aspects are usually handled by the travel agents.
Please provide more details like the country, approximate period of assignment, type of visa, whether you are going with or without family, etc. The more inputs you provide, the better and more accurate suggestions the members can offer.
Regards,
TS