Sorry Lexis, I am not a veteran but these tips may help a newbie. I wished I had listed to people giving this advice when I started.
For starters
If you are buying domains to flip for profit:
1. Stick to com/net/org/ It is harder to flip ws/cc/me/info etc so stick to what sells.
2. Buy product or service domains that there are numerous end users for. After you sell a few domains and get a feel for things try "Brandables" Don't buy 5L dot coms that sound "cool" and expect people to buy them immediately.
3. Don't follow the hype threads.
4.Don't get excited and buy too many domains. Buy one, flip it. Buy 5 more flip-invest-flip.
5. Use the free tools to evaluate domains. Google keywords etc
6. After you make some income invest in a drop list sorter (like freshdrop). Many people say all the good domains are taken and you have to buy on the aftermarket. That is true to an extent, but for someone (without a lot of capital) starting off they can find expired domains, especially with the help of services like freshdrop. I sold three hand regs this week 1 org $200, cost $7.50(Bulk pricing because of tip 4), one .net $250-cost $5.50 and currently negotiating a 3word dot come at around $625. These domains are between 10 and 100 days old. 2 were the result of sending end user letters and one was a direct inquiry. You can alos find aftermarket domains this way if you choose.
7. Price your domains realistically. Don't expect to hand reg a domain and flip it for a new car. There was a reason it was available. That doesn't mean that it has no value. It just means that it is not worth the big players regging and selling for a couple of hundred bucks. I hundred dollar profit for me is comparable to one of the Ricks make $10,000 on a sale.
8. Know your place and try to improve it. Big time players deal with big time clients. Small time players deal with small time clients. When you are starting out, you are a small time player. Having SkiResorts/me and thinking you are going to strike it rich beccause SkiResorts.com sold for around $800k is wishful thinking

Trust me.
Don't bother even trying to deal with big companies. Again, if they wanted the domain they would have it already. Find a small business with a worse domain and tell them why yours is better, Sell the domain at a price they can justify and make a profit.
9. Listen to the people on the boards but know how to judge. Look at the domains in their sigs, see what kind of domains they are selling. If the domains they are have in their sigs are domains that after a year of domaining you wouldn't consider regging or their listings and sales are primarily $28 infos through Bido take their advise sparingly. Nothing wrong with selling a domain for a profit anywhere, but if you are doing that after 5+, you are not progressing. There are some excellent members offer excellent advise here. It is important to read what is going on but after a while you get to know who to trust who not to.
10. Remember that it is a numbers game. From search volume to CPC to the amount of end user emails you send, its all about the numbers. For the most part, if your domains don't have the numbers, they won't sell. If you don't send the end user letters, your domains don't sell.
You are not going to get rich quick unless you are extremely lucky. Invest 10 make 100. Invest 100 make 1000. Invest 1000 make 10000. Rinse and repeat. Find a pattern or system that works and stick to it.
My biggest mistakes were points 1 and 4. If I knew then what I know now I would be years ahead of my current situation.