Does it need...?
│
├── useState, useEffect, event handlers
│   └── Client Component ('use client')
│
├── Direct data fetching, no interactivity
│   └── Server Component (default)
│
└── Both? 
    └── Split: Server parent + Client child

By Default

Type	Use
Server	Data fetching, layout, static content
Client	Forms, buttons, interactive UI

2. Data Fetching Patterns

Fetch Strategy

Pattern	Use
Default	Static (cached at build)
Revalidate	ISR (time-based refresh)
No-store	Dynamic (every request)

Data Flow

Source	Pattern
Database	Server Component fetch
API	fetch with caching
User input	Client state + server action

3. Routing Principles

File Conventions

File	Purpose
`page.tsx`	Route UI
`layout.tsx`	Shared layout
`loading.tsx`	Loading state
`error.tsx`	Error boundary
`not-found.tsx`	404 page

Route Organization

Pattern	Use
Route groups `(name)`	Organize without URL
Parallel routes `@slot`	Multiple same-level pages
Intercepting `(.)`	Modal overlays

4. API Routes

Route Handlers

Method	Use
GET	Read data
POST	Create data
PUT/PATCH	Update data
DELETE	Remove data

Best Practices

Validate input with Zod
Return proper status codes
Handle errors gracefully
Use Edge runtime when possible

5. Performance Principles

Image Optimization

Use next/image component
Set priority for above-fold
Provide blur placeholder
Use responsive sizes

Bundle Optimization

Dynamic imports for heavy components
Route-based code splitting (automatic)
Analyze with bundle analyzer

6. Metadata

Static vs Dynamic

Type	Use
Static export	Fixed metadata
generateMetadata	Dynamic per-route

Essential Tags

title (50-60 chars)
description (150-160 chars)
Open Graph images
Canonical URL

7. Caching Strategy

Cache Layers

Layer	Control
Request	fetch options
Data	revalidate/tags
Full route	route config

Revalidation

Method	Use
Time-based	`revalidate: 60`
On-demand	`revalidatePath/Tag`
No cache	`no-store`

8. Server Actions

Use Cases

Form submissions
Data mutations
Revalidation triggers

Best Practices

Mark with 'use server'
Validate all inputs
Return typed responses
Handle errors

9. Anti-Patterns

❌ Don't	✅ Do
'use client' everywhere	Server by default
Fetch in client components	Fetch in server
Skip loading states	Use loading.tsx
Ignore error boundaries	Use error.tsx
Large client bundles	Dynamic imports

10. Project Structure

app/
├── (marketing)/     # Route group
│   └── page.tsx
├── (dashboard)/
│   ├── layout.tsx   # Dashboard layout
│   └── page.tsx
├── api/
│   └── [resource]/
│       └── route.ts
└── components/
    └── ui/

Remember: Server Components are the default for a reason. Start there, add client only when needed.

nextjs-best-practices

Next.js Best Practices

1. Server vs Client Components

Decision Tree