I work in the tech sector.
A typical day starts with reading an in-depth briefing email. It lists mentions in the media of key people and topics of interest to my company (ministers, shadow ministers, backbenchers, campaign groups, charities, think tanks, government department announcements, etc). So for example, if you were lobbying for Tesco you'd be interested in anything to do with retail, food prices, cost of living and a load of other stuff.
I also get updated on anything that happened in Parliament the previous day - debates, legislation passing, relevant speeches etc. Same with regard to any local councils that might have announced something relevant. So my job involves a lot of reading.
After that I'm usually preparing for a meeting with a civil servant or politician, drafting documents like consultation responses or commissioning research to prove a point I'm trying to make. I also spend a lot of time working with people across my company so they are aware of announcements from the government and opposition and I explain how they could affect the business. Sometimes I spend time liaising with the trade association for my sector so we present a united front to government.
I'll always be looking out for new people to try and get to know or organisations to learn more about.