Short answer: you can reduce but not guarantee prevention. Websites link accounts using email/phone/payment info, IP address, cookies/local storage, browser fingerprinting, social logins, and account-recovery data. The most effective steps combine separating identities (different contact/payment info) with technical isolation (different browser profiles/containers, IP masking, and tracker-blocking).

Practical checklist (high impact → low effort)

1. Use distinct contact info

   • Different email addresses for each identity (use separate providers or an alias/forwarding service such as SimpleLogin/ProtonMail aliases). Don’t reuse the same primary email as a recovery address.
   • Don’t reuse the same phone number for account verification/recovery (use a burner number or separate number).
   • Use different names/profile photos where reasonable (and consistent with site rules).

2. Isolate browser storage and cookies

   • Use separate browser profiles or separate browsers per identity (Chrome profile, Firefox profile, Brave, etc.).
   • Easier: use Firefox Multi-Account Containers to isolate cookies/storage by site or identity.
   • Avoid relying on Incognito/Private mode alone — it only clears local traces after the session; it does not prevent cross-site linking while you’re logged in.

3. Block cross-site trackers and scripts

   • Install tracker/ad blockers and anti-fingerprinting extensions: uBlock Origin, Privacy Badger, Decentraleyes, Cookie AutoDelete.
   • Consider script blocking (NoScript or uMatrix-style) for sites you don’t trust — many linkers use third-party scripts and pixels.
   • Disable third-party cookies in browser settings.

4. Reduce fingerprinting and IP linking

   • Use a reputable VPN to change your IP when switching identities. Note: VPN providers can log; pick a no-log, trustworthy provider or self-hosted VPN if needed.
   • For stronger anonymity, use Tor Browser (but some sites block or flag Tor exit nodes, and Tor browsing may be inconvenient for accounts that require JS).
   • Disable or mitigate WebRTC to prevent local IP leaks (e.g., in Firefox set media.peerconnection.enabled=false; Chrome users can use a WebRTC-block extension).
   • Don’t customize browser in ways that make you unique (fonts, plugins, uncommon extensions) — being “too unique” makes fingerprinting easier.

5. Separate payment and shipping

   • Use different payment methods per identity (prepaid cards, separate credit cards, or privacy-preserving payment options). Be aware payment info is a strong linking signal.
   • For physical goods use different shipping addresses or mail-forwarding services if appropriate and permitted.

6. Avoid social/SAML logins and shared OAuth providers

   • Don’t use “Log in with Google/Facebook/Apple” across identities. Social logins create strong cross-site linkability.
   • Create separate login credentials for each account instead.

7. Watch account recovery and metadata

   • Don’t list the same recovery email or phone across accounts.
   • Avoid reusing usernames that are unique and used elsewhere.
   • Be mindful of shared profile data (birthdate, location, employer) that can tie identities together.

8. Operational security (advanced)

   • Use separate OS user accounts, virtual machines, or separate physical devices for strict separation.
   • Use containerized browsers or ephemeral VMs when creating highly separated accounts.
   • Consider fingerprint-resistant browsers (Tor Browser) or privacy-hardened Firefox builds and enable resistFingerprinting, but accept the utility trade-offs.

What won’t help (and common misconceptions)

• Incognito/private mode = local privacy only (it does not hide your IP or stop trackers while you’re logged in).
• Clearing cookies once a day doesn’t stop fingerprinting or linking via email/phone/payment.
• One VPN alone isn’t foolproof if you reuse emails/phones/payment or if the VPN leaks or logs.

Legal and policy notes

• Creating multiple accounts can violate site Terms of Service — that can lead to bans or legal issues. Use these techniques for legitimate privacy reasons (e.g., separating work/personal accounts, testing, protecting a pseudonymous identity), not for fraud or evasion of bans.

Quick recommended setup (simple, effective)

• Email: separate addresses (use an alias/forwarder).
• Browser: use Firefox with Multi-Account Containers + uBlock Origin + Cookie AutoDelete.
• IP: use a reputable VPN or separate network when switching identities.
• No social login; unique payment/recovery info.

If you tell me what level of convenience vs anonymity you want (easy everyday separation vs strong un-linkability), I can give a tailored step-by-step setup for your devices and browsers.