Sometimes you'll know what you're searching for (i.e. Nanette Lepore Usual Suspects Dress size 2) and sometimes you won't (i.e. Black pants size 10). Either is fine. I like to search by brand names because then I'm searching brands that I know fit me and I can feel confident that I will like whatever I receive.
I think that's probably the best place to start. When I started on eBay I would generally only buy from brands I knew - brands I knew my size in, brands I knew my fit in, etc - until I developed some confidence in buying online and started branching out. I measured clothes I owned that fit me very well and compared these to the given measurements of eBay items. I measured myself and checked size charts for different brands online to be sure of my size. Knowing that what you buy will fit is the most important part of any transaction - you can get a really great deal on a really nice pair of pants, but if they don't fit then you're not going to be wearing them, in which case they weren't really a good deal at all.
your search screen
So let's say you really like Phillip Lim, but know he just came out with a collection for target and don't want to just see a ton of that stuff (after all, those things are cheap already!). Just like in Google, you can use the quotation marks to specify a specific phrase (like "Armani Collezioni" so you don't get a bunch of Armani Exchange stuff), the "+" to specify inclusion of a certain word, and the "-" to specify that your search results should not contain a certain word.
In this case, we search for "Phillip Lim -target" because we want Phillip Lim but we don't want Target results. Now some will still seep through - some sellers deceptively label their "Phillip Lim for Target" items as regular "Phillip Lim", but hopefully there will be pictures of the inner tag so you can be sure of what you're buying, and if for any reason you're not - don't buy it.
Other cases where the "-" is very useful, for me anyway, are in bag searches for brands that make cosmetics, and for St. John clothing which is definitely very different from St. Johns Bay even though apparently eBay doesn't think so. You'll see in a bit that my search for "Balenciaga Clutch" contains the terms "-perfume", "-gift", "-parfum", "-canvas" because apparently Balenciaga perfumes gives out teeny tiny mini "clutches" with purchase, and people put these on eBay to be sold calling them "Authentic Balenciaga Clutch"es.
Before you start looking at the clothes, you should first set up your search parameters. At the top of the above pictured screen, you can see that you can specify buying format - All Listings, Auctions, or Buy It Now. Your best deals are generally going to be found in the Auctions section, but I typically keep "All Listings" just because youo never know when you'll find something good at a good Buy It Now price. Just the other day I found a really cute brand new Torn by Ronny Kobo dress with a Buy It Now price of $20, something I wouldn't have found had my searches been Auctions only.
Next is the sidebar, alongside the searches. Here you can specify lots of things. The most important is usually the category, in which you can select "women's clothing" or "men's clothing" to be sure you're only getting things you want. The next most important is the "Condition" section, near the top of the continued sidebar. This allows you to check off "New with tags" and "New without tags" to specify that you are only looking at items that are new and never worn. I do this with most of my searches, although with the more expensive brands I typically don't.
The reason these two are most important is that eBay lists them separately when you are selling, forcing you to put thought into selecting them. The other categories are either optional when listing or lumped together and typically ignored, so even though you can specify your size, I think you are better off putting the size in the search (i.e. "Phillip Lim M -target" if you want mediums) than specifying on the sidebar.
back to the top
Once your search is properly set up, you can choose how to sort your results. I sort almost everything by Price + Shipping: lowest first. The default is best match, but if you stick with that you're likely to see some really high prices and get discouraged right away. When you sort by lowest price, you're likely to see some weird stuff down there, but there's also plenty of good things.
Now that all your options are set, you click "Follow this search" to save the search. This is advantageous particularly if you use the eBay app on your phone. Not only are you saving your search for ease of finding it and searching the same thing later on, but on your phone you can also search through only the newly listed items since you last performed the search.
Here, the blue dots signify that new items have been listed since the search was last checked. When you open a search with this blue dot, only newly listed items are shown, meaning you aren't scrolling endlessly through the same items every time you open your search. Now you'll be viewing all the newly listed items of a particular search in ascending price order.
your saved searches, online
To find your saved searches, go to "My eBay" and then click the "Searches you follow" link along the lefthand side to view them all. From here you can manage email notifications when new items are posted within your searches and delete ones that aren't relevant to you anymore. There is a maximum of saved searches you can have but it's very high.
So now you've done your search and found some items you're interested in, so the next step is to watch this item. This way you can keep track of it as the price changes and then bid (or, preferably, put a snipe in Gixen!) appropriately.
an item worth adding to the watch list
You can access your watch list from My eBay, similar to how you access your followed searches.
This item is pretty nice, so you might want to see what other items this particular seller has, and if they have good things, follow them so you can easily see when they post new items.
saving a seller, and seeing their other items.
For sellers who have massive inventory, BHFO for example, you can search only their inventory on your computer by clicking the "see other items" option and then typing in what you want to search for in the search field. By doing this, you can skim through a particular seller that you have confidence in and trust's items.
On your phone app, the format for searching a particular seller's items is "seller:bhfo nanette" if you want to search items with the word "nanette" in the title from the seller BHFO.
This probably seems like a lot of info all at one but it's really all very easy once you get the hang out it, and you'll be blown away by the prices you can get on things that come to you new with tags or in excellent condition.
I hope this was helpful to some of you. If you have any further questions about anything please feel free to leave them in the comments of email me, I'd be happy to help you out on your shopping adventures!