not hard at all. usually you apply jobs and doing interviews on F1. Once landed a job, discuss a starting date with the employer and apply for opt, might take 4 months. once have opt, you can start.

once start, you can apply for h1b. the time for filing h1b is April, so ideally you should land a job offer before April, otherwise you will have wait for April of the next year.

bigger companies are more likely to sponsor h1b, whereas smaller ones and startups will probably won't do it. there are requirements on the ratio of citizen employees vs foreigners and minimum payment, smaller companies usually won't be able to meet the requirement.