Unity Coding Guidelines

TheThing.cs

using UnityEngine;
using System.Collections;

namespace CompanyName {
    
    public class TheThing : MonoBehaviour {

        // 1
        // Public fields section. Try to avoid public fields.

        public int SomeValue; // Avoid public fields. Use public properties instead.
        public static int SomeGlobalValue; // Avoid static fields.

        // 2
        // Unity inspector section

        [SerializeField] Transform _otherTransform = default;
        [SerializeField] float _someValue = default;

        // 3
        // Protected section

        protected int _someValue1;
        protected const float SOME_VALUE = 0f;

        // 4
        // Private section

        int _someValue2;
        Vector3 _someDirection = Vector3.up;
        static int _someGlobalValue2; // Try to avoid using static fields.

        // 5
        // Properties section

        public int Value { get; private set; } // Use public auto properties if needed.
        public float Value2 => _someValue + SOME_VALUE + CalculateSomeValue();

        // 6
        // Class methods. Use public only if you can't

        float CalculateSomeValue() {
            // Bad example of method (In this particular code property works better)
            var retValue = _someDirection.magnitude;
            return retValue;
        }

        public void MoveUp() => StartCoroutine(_MoveUp());

        IEnumerator _MoveUp() {
            for(var i = 0; i < 10; i++) {
                _someDirection += Vector3.up * 0.1f;
                yield return new WaitForSeconds(0.1f);
            }
        }

        // 7
        // Unity stuff.

        void Start() {
            var a = 10; // Use var!
            for(var i = 0; i < a; i++) {
                Debug.Log($"i = {i}"); // Use string interpolation.
                Log.Message("i = {0}", i); // Custom log without interpolations and allocations is better.
            }
        }

        void Update() {
            // Don't write/leave empty methods. Leads to performance lack.
        }

    }
}

Real code/class example without guidelines comments.

using UnityEngine;
using System.Collections;

namespace Company {

    public class TheRealThing : MonoBehaviour {

        [SerializeField] Transform _otherTransform = default;
        [SerializeField] float _someValue = default;

        int _someValue2;
        Vector3 _someDirection = Vector3.up;
        const float SOME_VALUE = 0f;

        public int Value { get; private set; }
        public float Value2 => _someValue + SOME_VALUE + CalculateSomeValue();

        float CalculateSomeValue() {
            var retValue = _someDirection.magnitude;
            return retValue;
        }

        public void MoveUp() => StartCoroutine(_MoveUp());

        IEnumerator _MoveUp() {
            for(var i = 0; i < 10; i++) {
                _someDirection += Vector3.up * 0.1f;
                yield return new WaitForSeconds(0.1f);
            }
        }

        void Start() {
            var a = 10; // Use var!
            for(var i = 0; i < a; i++) {
                Log.Message("i = {0}", i);
            }
        }

    }
}