I know this is a bit OTT but i really works for me, to stat by writing a list of outfits required. In a spreadsheet, so a column for each type of thing required, top, bottoms, underwear, accessories, shoes ...
First time through each row, it's just general terms so top1, trousers1, plus anything special say rainproof overcoat, or shoes i can walk in. Swimsuits, ski gear etc. Then fill up with identified pieces, spread them out over the bed or something so you can see what goes with what. Ideally, have colours and style done so eventually, you only have clothes you love in your own colour palette. How to ring the changes with essentially the same dress with different accessories. Just make sure you are prepared for disasters, like spilling something on the trousers. You probably need two pairs, rather than just one. One to wear and one for spare..
This shows you what you need to get, say new trousers and/or things you would like to add. Make sure you start with plenty of time, to try everything on in outfits, spot anything that needs mending, or cleaning, or is more threadbare than you expected.
Now you are ready to work out how to make savings, if you take those trousers, you have enough tops to go. Just need one More pair of dressier evening trousers, strappy sandals and you are done. Plus no need to think what shall i wear on holiday, its all planned.
Enjoy.
The more times you do this, the easier to becomes. I leave everything out in the spare room, add or take away as required. If you travel a lot, get a spare set of toiletries, buy new as you get to the last say quarter to build up your stock. Night before, put everything into the case, add toothbrush the next morning, do it up and you are ready. Spare undies in your hand baggage if you are flying..sorted.