Patterns of Play
You should aim to gradually build up a database of shots that can be grouped together into small scoring patterns of 2-5 shots. Thereafter, by combining 2 or 3 of these small scoring patterns you will be able to make larger patterns of play that will easily enable you to make 30+ breaks. Eventually these patterns will all merge together to produce the 'game' or the overall pattern that you play.
To be a good player you do not need to be a master of all strokes, but you do need to understand your strengths along with your limitations and play accordingly. Disregard those who say that you should always play the 'right shot'; there is no such thing as a 'right shot' in Billiards, only a right shot for you at your current skill and experience level. There is no point in including nursery cannons in your game until you can get the balls into position for close cannons, and then more importantly be able to play them. Pick the shots that you can play and as your skill level increases you will be able to add more shots to your repertoire and change your pattern accordingly.
Once you have sufficient skill to play the individual shots and can utilize them by incorporating them into patterns and eventually your 'game', you need to have an overall strategy or purpose. Championships have been won using many Strategies, which include patterns as varied as Postman's Knock, Losing hazards and the Floating White. If you have a purpose, a principal method of scoring, it will focus your mind. A Billiards match will not always go as planned and you will often be left with awkward leaves. If you have a strategy for play it can help you overcome difficulties.
Keep a record of your progress and breaks as this will allow you to measure your improvement. When you play a game with a friend, record the number of visits so that you can take the average score for each visit. Your 'AVERAGE' is the best way of determining your standard and your improvement. These recorded results will give you encouragement to practise and improve.
Ideally you would become a master of all strokes and be able to alternate freely from open play, top of the table, cannons and then back to open play without incurring any significant risk. Realistically, this is out of the reach of most of us but you will still achieve great satisfaction and enjoyment at Billiards by playing YOUR game and making improvement as time goes on. Setting your own targets and achieving them can be very satisfying. Try to make sure that your targets are realistic and achievable, but require some effort.
Try to get the balance right during your practice. It is no use repeating shot after shot and doing nothing else if you are not enjoying it. Perhaps choose a couple of shots and work at them along with playing friendly games now and then to see what shots come along and make a note of what you need to work on. Most players will become more accomplished if they complete some solo practice. Billiards is a beautiful game and should be enjoyed, so try to get the balance right for you.