I spend quite some time using psql during my day, and over time I've found some nice things that make my workflow better:

Variables

You can set variables using \set, this is helpful in cases when you need to run the same query over and over again (for example, during some exploratory analysis) with different input parameters.

\set question '''The answer to life, the universe and everything'''
\set answer 42

select :question as question, :answer as answer from generate_series(1,5);

select :question as question, :answer as answer from generate_series(
                    question                     | answer 
-------------------------------------------------+--------
 The answer to life, the universe and everything |     42
 The answer to life, the universe and everything |     42
 The answer to life, the universe and everything |     42
 The answer to life, the universe and everything |     42
 The answer to life, the universe and everything |     42
(5 rows)

You can also store the result of a query in a variable using \gset:

select 42 as answer \gset
\echo The answer to life, the universe and everything is :answer.
The answer to life, the universe and everything is 42.

Use \unset to delete a variable.

Formatting

You probably know that \x enables the expanded display mode:

\x
Expanded display is on.
select md5(random()::varchar || current_timestamp::varchar)::uuid uid,
    'Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod
     tempor incididunt ut labore et dolore magna aliqua.
      Ut enim ad minim veniam...' lorem;
[ RECORD 1 ]-------------------------------------------------------------------------------------------------------------------------------------------------
uid   | 4be8d427-c0f5-448a-1686-b91bd4f61667
lorem | Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam...

But using \pset format wrapped you can keep the column mode and have a "nicely" formatted output:

\pset format wrapped
\pset columns 80
select md5(random()::varchar || current_timestamp::varchar)::uuid uid,
    'Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod
     tempor incididunt ut labore et dolore magna aliqua.
      Ut enim ad minim veniam...' lorem;
                 uid                  |                  lorem                  
--------------------------------------+-----------------------------------------
 de21cb74-e79f-b9d4-ff70-8e0b04a0e0b2 | Lorem ipsum dolor sit amet, consectetur.
                                      |. adipiscing elit, sed do eiusmod tempor.
                                      |. incididunt ut labore et dolore magna a.
                                      |.liqua. Ut enim ad minim veniam...
(1 row)

Making Your Life Easier

Execute a query every n seconds using \watch:

# select random() \watch 1
mon 01 mar 2021 20:50:13 CET (every 1s)

      random       
-------------------
 0.592619172297418
(1 row)

mon 01 mar 2021 20:50:14 CET (every 1s)

      random       
-------------------
 0.760892618447542
(1 row)

mon 01 mar 2021 20:50:15 CET (every 1s)

      random       
-------------------
 0.498985073994845
(1 row)

mon 01 mar 2021 20:50:16 CET (every 1s)

      random       
-------------------
 0.157784981653094
(1 row)

mon 01 mar 2021 20:50:17 CET (every 1s)

      random       
-------------------
 0.850564768537879
(1 row)

You could write anonymous functions to do things like creating or truncating multiple tables at once:

DO
$$
BEGIN
FOR c in 65..70 loop
 EXECUTE 'CREATE TABLE sample.'|| chr(c) || '()';
END loop;
END$$;

DO

DO
$$
BEGIN
   EXECUTE
	(SELECT 'TRUNCATE TABLE ' || string_agg(table_schema || '.' || 
    table_name, ', ') || ' RESTART IDENTITY CASCADE'
		FROM information_schema.tables 
		WHERE table_schema in ('sample')
		);
END$$;

DO

Or, you could use \gexec to execute the results of the query:

select 'CREATE TABLE sample.' || chr(generate_series(65, 70)) || '()' \gexec

CREATE TABLE
CREATE TABLE
CREATE TABLE
CREATE TABLE
CREATE TABLE
CREATE TABLE

SELECT 'TRUNCATE TABLE ' || string_agg(table_schema || '.' || 
    table_name, ', ') || ' RESTART IDENTITY CASCADE'
		FROM information_schema.tables 
		WHERE table_schema in ('sample') \gexec

TRUNCATE TABLE

Conclusion

There are quite some useful things that can be found using the help (\?) command in psql, it's not the worst idea to go give it a look.