See here for templates that might help pull somethings together:
https://www.smartsheet.com/free-onboarding-checklists-and-te...
Assuming you have HR/IT set up and onboarding guides done and the general intro to company stuff set up etc: I have found the following to be helpful to getting team productive but your mileage may vary:
For engineers -intro projects with assigned mentor. short project (from few days to a week) on a specific small feature that is designed to take them through all tooling, codebase and environments that you use. Idea is to expose new hire to development environment in a controlled way, give them a chance to learn, document their frustrations/questions, discover who to ask, how to ask (e..g do you use slack, in person etc), how peer and code review are done etc and get them productive with a win that contributes to the product.
It takes time to set up - but its worth while and if you know your onboarding - its easy enough to review sprint plans and id suitable tasks ahead of time and after you do it a few times it becomes routine and expected.
For marketing team - similar usually get them to review a marketing plan in an area they are going to be working in and how that fits across marketing tools and evaluate it and present insights back to team at following weeks marketing meeting. Same idea - expose them, get their insights and get them talking with their team and have them work on something that is needed.
For sales team - take them through structures sales training: Product, customer value prop, competitive analysis, target customer profiles, critical problems we solve, scenario role play finishing with sales and product qualification (ie have a test they must pass so you know they have a minimum level of product and target customer knowledge)
For all new hires assign a mentor - person who will help them through their first week and first weeks tasks. At end of on boarding Ask new hires to rate their mentors and the onboarding process - you want your onboarding experience to be positive for everyone and you want it to get better.
You will be tempted to have recent hires mentors the next in- since many things will be fresh in their memory- this works but its also useful to remind established folks what entry is like and expose senior team to new team members and map mentors to incoming expertise (e.g. some senior engineers may know a specific area of codebase so will be a better mentor for that position etc) so don't do it exclusively.
with any new hire - do a end of day 1, mid week and end of week check in to make sure all is going ok and they have opportunity to ask questions/follow up (it is surprising how many HR questiosn come up on day 4).
This sounds like a lot - but its worth investing in it. Most onboarding sucks - it shouldnt.