docs: add guidelines around imports and initializing GAPIC objects (#6582)

* docs: add guidelines around imports and initializing GAPIC objects

* Apply suggestions from code review

Co-authored-by: Leah E. Cole <6719667+leahecole@users.noreply.github.com>

Author: busunkim96

AUTHORING_GUIDE.md

@@ -171,6 +171,84 @@ comments and docstrings only as needed to further clarify the code’s intent.
 Always introduce functions and variables before they are used. Prefer less
 indirection. Prefer imperative programming as it is easier to understand.
 
+
+### Importing Google Cloud Libraries
+
+Follow this style for importing Google Cloud libraries:
+
+```py
+from google.cloud import texttospeech_v1
+```
+
+All commonly used clients and types are exposed under `texttospeech_v1`.
+
+```py
+from google.cloud import texttospeech_v1
+
+client = texttospeech_v1.TextToSpeechClient()
+
+audio_config = texttospeech.AudioConfig(
+        audio_encoding=texttospeech.AudioEncoding.MP3
+)
+```
+
+
+### Creating Request Objects for GAPICs
+
+GAPIC libraries are generated from [protos](https://github.com/googleapis/googleapis)
+that define the API surface via a [generator](https://github.com/googleapis/gapic-generator-python).
+GAPIC libraries have library type `GAPIC_AUTO` in `.repo-metadata.json`
+located in the root of the repository. Some `GAPIC_COMBO` libraries will
+also expose [`proto-plus`](https://github.com/googleapis/proto-plus-python/) types.
+
+Because they are generated, GAPIC libraries share a common interface.
+All API proto messages are exposed as `proto-plus` message classes.
+
+`proto-plus` provides a [few ways to create objects](https://proto-plus-python.readthedocs.io/en/latest/messages.html#usage).
+
+Strongly prefer instantiating library types through the constructor
+or by instantiating an empty object and initializing individual attributes.
+The dictionary construction method is discouraged as it is harder to use
+type checking and IDEs are not able to offer intellisense.
+
+```py
+# To try this sample yourself, install `google-cloud-tasks==2.5.1`
+from google.cloud import tasks_v2
+
+
+# 1. Generated types via constructor
+task_from_constructor = tasks_v2.Task(
+    http_request=tasks_v2.HttpRequest(
+        http_method=tasks_v2.HttpMethod.POST,
+        url="https://pubsub.googleapis.com/v1/projects/my-project/topics/testtopic:publish",
+        body=b"eyJtZXNzYWdlcyI6IFt7ImRhdGEiOiAiVkdocGN5QnBjeUJoSUhSbGMzUUsifV19Cg==",
+        oauth_token=tasks_v2.OAuthToken(
+            service_account_email='my-svc-acct@my-project.iam.gserviceaccount.com'
+        )
+    )
+)
+
+# 2. Instantiate object and then set attributes
+http_request = tasks_v2.HttpRequest()
+http_request.http_method = tasks_v2.HttpMethod.POST
+http_request.url = "https://pubsub.googleapis.com/v1/projects/my-project/topics/testtopic:publish"
+http_request.body = b"eyJtZXNzYWdlcyI6IFt7ImRhdGEiOiAiVkdocGN5QnBjeUJoSUhSbGMzUUsifV19Cg==",
+http_request.oauth_token.service_account_email = "my-svc-acct@my-project.iam.gserviceaccount.com"
+
+task = tasks_v2.Task()
+task.http_request = http_request
+
+# 2. Dictionary (NOT RECOMMENDED)
+task_from_dict = {
+    "http_request": {
+        "http_method": "POST",
+        "url": "https://pubsub.googleapis.com/v1/projects/my-project/topics/testtopic:publish",
+        "body": b"eyJtZXNzYWdlcyI6IFt7ImRhdGEiOiAiVkdocGN5QnBjeUJoSUhSbGMzUUsifV19Cg==",
+        "oauth_token": {"service_account_email":"my-svc-acct@my-project.iam.gserviceaccount.com"},
+    }
+}
+```
+
 ### Functions and Classes
 
 Very few samples will require authoring classes. Prefer functions whenever