A few things I've noticed help small agencies/solo businesses once deals start slipping through the cracks:

Keep company info, contact info, and the deal itself linked not spread across a spreadsheet, your email, and your notes app

Have one view that shows every deal's stage at a glance, so nothing needs "checking in on" from memory

Track deal value somewhere, even roughly knowing your pipeline's worth changes how you prioritize your week

If you're a solo owner and a paid CRM tool is just out of budget right now, I build Notion CRMs and I'm happy to send mine over free genuinely, no strings, just comment or DM if that's useful to you