Tank size, lighting and flow are also important elements to what is easy and what is difficult. Lots of flow can make LPS more difficult. Too much light can be deadly to coral as too little can as well. Yellow tangs can be easy to keep in the right size while in a tank that's too small they will stress and could come down with ich and will likely becoming even more aggressive.
However, some good rules of thumb for what is easy
1) Aquacultured/captive bred fish and coral: Have been acclimated to living in captivity and are therefore more hardy than their wild caught counter parts
2) Soft corals: Hardy, grow quickly and can come in a wide variety of colors (downside is they can be extremely competitive with stony corals so proceed with caution, however they are still great for first tanks when you don't know what you want)
3) SMALL FISH: Cardinals, clowns (can be aggressive but usually stake out a place and stick to it), hardy wrasse species (stay away from flasher and fairy), dotty backs, gobies and firefish (if you don't have a top beware they are jumpers, as are the wrasses) and chromis will typically be your best fish
-Small fish to avoid (dragonets aka mandarin gobies aka scooter blennies, non reef safe wrasse, blennies just because it is hard to tell which ones are reef safe as a beginner, dwarf angels)
4) Avoid anemones: just do it, trust me when you are ready for one you will be glad you waited
5) Only get plain-jane nassarius snails and small hermits such as blue leg for cleanup crew: starfish can be tricky, big hermits and crabs tend to knock things over and fancy snails can be dangerous
But most importantly don't try to jump into this hobby and compete with tanks that win Tank of the Month awards. Unless you are willing to shell out 10,000 right away you are going to be frustrated if you try to do this. Start with a simple setup, learn about equipment, learn how to monitor your tank but most of all start with a tank that is easy because it will allow you to enjoy the hobby. I've watched too many people jump into the hobby and spend (and lose) a considerable amount of money only to get out of the hobby 6 months later when their tank crashes because they put a powder blue in with 2 yellow tangs and everything catches ich. It is much less frustrating to melt a 15 dollar frag of eagle eye zoas than to lose a 200 dollar scoly.
Anyways that's my rant, long story short if it is your first tank look for what is simple rather than looking for what to avoid and remember longevity is the truest sign of success in this hobby. Research before you buy, plan how you want to do your tank (post your tank setup and a planned stocking list and I guarantee you will get help) and do your best to avoid the fish store impulse buy (we are all guilty of this but do your best!).
Good Luck!