Here's a few hints on it:
1. Make a list
The definition of being organized usually starts with a list. Make a list of everything you wish to take along with you on your holiday at the beach or the mountains, etc. It should include categories such as clothing, shoes, toiletries, but also documents, maybe even a map if it's the case, reading material, and the info of your accommodation. Try not to forget items such as toothpaste, sunglasses, pajamas, socks... it's been known to happen in many cases. Keep into account the weather and what your activities will be.
2. Choose your clothes wisely... and in advance
It's much easier if you plan your outfits in advance. If you though do not quite feel inspired to do so, choose clothing that will allow you to adapt to various conditions. A few examples are a cardigan or light jacket that matches several tops, jeans that you can roll up, etc. Also try layering, it never fails. Bring some platic bags for dirty items too.
3. Pack the heavy stuff at the bottom
Any thick clothing that obviously takes up amore space should be placed at the bottom of your suitcase. You can also opt for compression bags, which will help you save up a lot of space. Adopt the "rolling" technique, meaning place a few clothes one on top of the other and roll them up like a sleeping bag. This way they won't get wrinkled and again... they take up less space.
4. Travel-sized cosmetics
You don't need to pack up too many toiletries, especially if you won't really travel to somewhere at the end of the Earth or so. Most likely you will find a store where you can restock your supply of some of these if needed.
5. Take a first-aid kit with you
You don't need too much medicine, but some pills that can help you out in case of headache, fever, cough, etc. may turn out to be of great help after all. In a foreign country certain medicine may only be available on prescription, and this may get things complicated.
6. Pack chargers and adapters
You can stick them inside the shoes you pack actually, to save on space. Chargers for your phone, camera, laptop if it's the case, headphones, etc. may come in use. Adapters and converters are important too, so you make sure your electronics can be charged.
7. Snacks and entertainment
Taking along some snacks for in case you get hungry is a good idea, as is having a book or magazine on you. Traveling can often involve long periods of waiting and sitting around on a plane, in the car, on a train or bus and so on. You're gonna want to have the option of "looking busy" if you're not quite in the mood to chat with the person next to you. A book or a magazine can solve that pretty fast.
8. A money belt might be useful
Depending also on where you travel, a money belt may make things easier. You can carry it around your neck or around your waist and this way you know your valuables are safe.
9. Photocopies
This includes photocopies of important documents, including passport, prescription medications, important phone numbers, bank numbers, etc.
10. A big scarf
This can be much more useful than you imagine. Women can wear it as a skirt, at the beach, you can fold it up and use it as a pillow, it can make a comfy blanket and it will cover you up when you wish to enter into temples in places.
Always remember when packing that less is actually more, and the lighter your bags are the easier and the more enjoyable the trip will be. Whether you choose a holiday at the beach or a holiday among nature somewhere, make sure you carefully check what your accommodation has to offer as well, so you don't end up taking along unnecessary items. Go casual, simple and light, and if you're having second thoughts about packing an item, just leave it. This will also give you the perfect excuse to check out local department stores if needed.
Other than that... enjoy your travels! Remember they are a time for fun, relaxation and adventures, so make the best of it.
