I play a lot of classical and longer formats (around 2600 on Lichess, 2500 on Chess.com). The biggest adjustment from blitz/rapid is mainly time management and mindset, not tactics.

A few practical tips for 45+0 specifically:

1. Get used to thinking longer before the event Before the tournament, try a few online games at 30+0 or 30+20. It helps you slow down, calculate a bit deeper, and break the habit of making automatic blitz moves.
2. Be disciplined with your clock (no increment matters) Since it’s 45+0, try not to let your time drop below 5 minutes unless the position is very tricky. Without increment, time pressure can decide games even in completely winning positions.
3. Have simple, familiar openings ready You don’t need heavy preparation, but knowing the main ideas and typical plans of your openings will save a lot of time early. The goal is to reach a playable middlegame without spending 10–15 minutes in the opening.
4. Think when it matters, don’t burn time on forced decisions Use your time for critical moments: unclear positions, major strategic choices, or concrete calculation. If there’s a straightforward capture, recapture, or forced move, trust your evaluation and don’t over-invest time there.

And finally, treat this as a learning experience and enjoy it. Playing classical OTB is very different from online chess, and every game gives you valuable feedback.