I am a minimalist.
I'm not some lifestyle guru or diehard, but over the last several years I've been able to recognise patterns of behaviour in myself, understand how they align with minimalist philosophies, and then use that outlook to affect positive changes (often just small ones) and make my life better. Minimalism is most regularly approached from the perspective of needing less, and possessing enough but not too much. While this is important it's really just one practical exercise for contributing to the more meaningful goal, which is that of simplification. Minimalism, in one sense, is about making much of your life simpler so that you have greater resources to apply to those things that make your life happier. Of course, understanding the things that will bring you real and lasting happiness is another difficult question all on its own.
One way of reducing complexity in life is to reduce choice. Humans are awful at making choices, in particular when there is an overabundance of options. Marketing experts understand this as decision or choice paralysis, where the number of variations of an item is sufficiently great that the deliberation process becomes incapacitating and the choice is either made laboriously or avoided altogether. We are, of course, more than able to bring this problem upon ourselves. I'm sure you've had the experience of rooting through a well stocked pantry or refrigerator unable to decide from the many options in front of you just what it is that you actually want for dinner. It's why, despite having a bulging wardrobe, the cliche of having nothing to wear is a true life event. If you are more deliberate about the options you present to yourself then there is a sweet spot between variety and restriction (you want fewer, but not necessarily the minimum) where you will always have enough, but never so much that you're plagued by indecisiveness. You have to think ahead, be disciplined (but not overly strict), and understand that allowing for fewer choices maximises the quality of each of those choices. If you only keep three shirts, then all three are going to be shirts that you love, not shirts that are merely good enough.
The task therefore is to train yourself to apply some manner of internally consistent value system by which to make informed and deliberate decisions. That value system should also allow you to break the restrictions you put on yourself when something that is in one sense superfluous also has a high personal value. This might be an object that has to practical purpose, or has lost its purpose, but still holds significant sentimental or emotional meaning for you. Or it might be a collection of items of which you have more than you could justify in terms of necessity but the collection itself is a source of satisfaction. We all have those things that we do not require, but bring some enjoyment into our lives; minimalist philosophy does not necessarily exclude those, but it should ask you to consider them thoroughly. This system of ascribing value is going to be individual, and its success will hinge upon your ability to be honest with yourself. It's not going to be perfect — you'll have to feel your way through some of it, but try and be strict with yourself.
This isn't a practice limited to physical objects, either, and can be applied to other facets of life. The personal and professional projects you take on, or your hobbies. You have a finite resource in the time available to achieve the things you want to achieve, so those things with the greatest meaning, necessity, or value should take priority. You have to say no to the things that fill up your time but don't really matter to you. That doesn't mean you exclude all the small and less significant tasks, necessarily — sometimes you do not have the freedom to, or have responsibilities that override your personal priorities. It does mean that you will benefit from deliberate planning and avoiding patterns of behaviour that are ultimately less satisfying.
Having choice is a good thing on the whole, and a privilege, but it can be useful to limit that choice, to rule out quickly those options that are not attractive enough to invest in. Keeping choices simple will ensure you spend the minimum resources on them (and research suggests that choices get harder throughout the day and according to the frequency with which you have tho make), so you can focus more on the parts of your life that make your life better. You can figure our the things that make you happy and centre them in your decision making which will allow you to be more decisive, and also to spend more time doing the things that make you happy and with less anxiety about being able to do the things you can't avoid.