ONLY THOSE WHO CAN START NOW: MAKE A FULL BACKUP (files + DB) before starting. 2) Work environment: create a staging/clone and work there (never in production). Rollback procedure: take a snapshot before making critical changes. 3) Primary diagnostics: check PHP/Apache/Nginx logs and server system errors. Browser console (JS errors) and tests: Lighthouse/PageSpeed/GTmetrix. Anti-malware scans (Wordfence, Sucuri) and core file integrity checks. List outdated plugins/themes and recent changes. Database check: table sizes, transient data. 4) Fixing functional errors: Eliminate warnings/notices/fatal PHP: find the problematic file/plugin and fix the code or replace the plugin. Recovering missing images: check paths, file permissions (644/755), rewrite rules and hotlinking. Fixing corrupted CSS/JS: isolate conflicts (disable plugins one by one), correctly register scripts/styles. - Fixing 404 errors: check permalinks, regenerate .htaccess, set up correct 301/302 redirects. - Check responsiveness and fix display issues on mobile devices. 5) Images and Media - Convert/serve WebP with fallback for incompatible browsers. - Resize images to actual display dimensions. - Compress images (ShortPixel, Imagify, or equivalent). - Enable lazy loading (native or plugin). 6) Performance - Cache: server-side (OPcache, Varnish) + WP plugins (WP Rocket, LiteSpeed Cache, W3 Total Cache). - Minify/concatenate CSS/JS (check for conflicts). - Use defer/async for non-critical scripts. - Implement critical CSS for the area above the fold. - Reduce external requests (fonts, embed); store fonts locally or use preconnect. - Configure CDN and Cache-Control headers, gzip/brotli. - DB optimization: delete old revisions, transients, unused tables; optimize indexing. - Check TTFB and slow resources. 7) Security and Updates - Update core/plugins/theme first in staging, then in production. - Scan for malware and perform basic security enhancements. - Set up two-factor authentication, limit login attempts, and, if possible, whitelist admin IPs. - Check file and folder permissions. 8) Testing and Handover - Test in major browsers on desktop and mobile devices. - Provide a report: list of fixes, changed files, open/closed tickets. - Performance results before/after. - Describe steps for ongoing maintenance and recommendations to prevent the issue from recurring. - Provide estimated deadlines for each task and an overall delivery date. Prioritization: First: fix critical issues that hinder site performance (pages/images, irreversible errors). Then: speed optimization and general cleaning.