叫牌体系很难说哪个先进，哪个不先进。对于非职业牌手来说，应该优先选择当前最流行的叫牌体系比较好。

2/1和标准自然体系的最大区别不过在于2盖1进程之后是逼叫到局还是只逼叫一轮，以及由此带来的其他调整，所以他们本质上是相似的。

根据我所了解的目前打2盖1的牌手中最主流的趋势，我会设计这样一个2盖1体系：

1、5542开叫。即5张高花开叫；1D通常保证5张以上，除非是4441的牌型；1C开叫只保证两张（或者说：所有真C套的非均型牌和其他所有非NT开叫范围的均型牌）
2、1C开叫之后用T-WALSH，也就是应叫人用转移答叫。
3、大量使用转移叫来获取额外的叫牌空间，包括在竞叫序列中。比如：1H-1N-2S; 1M-1N-2N; 1N-(2M)-; 1M-(DBL)-; 1m-1M-2N; (1X)-1Y-(ps)- 等。
4、使用大量的人工叫牌约定来处理标准自然体系中叫牌难题。比如使用Kaplan Interchange 来解决开叫人4=5=x=x 牌型在 1H-1NT后的再叫困难。其他如Gazzilli, Reverse Flannery Response 等。
5、采用多义2C应叫或其他办法解决一阶高花开叫后，应叫人持均型逼局实力牌的应叫问题，目的是避免歧异的2C或2D应叫。
6、1M－1nt，1nt为semi-forcing，也就是开叫人持均型低限牌可以pass。
7、2盖1进程之后，所有的跳叫叫品都应该是严格定义的picture bid。
8、进局逼叫进程之后，并且高花3阶以下得到配合，使用seirous-3nt或者frivolous-3nt，以及last train来区分牌力，以提高满贯叫牌的准确性。

至于看什么书不叫好，早期的 Hardy 或者 Lawrence 关于2盖1的书可以作为入门，但由于内容过于陈旧，用处确实不大。而这些年很少有关于叫牌体系的书出版。

以我自己学习2盖1叫牌的体会（我早期打的是精确，对自然一窍不通），利用互联网上的资料基本够了，特别是如果你能常上BBO打牌，从BBO BASIC 或 BBO 2/1 入门起步，很快就会掌握自然叫牌基本结构。

提高桥牌水平的最重要，也是最便捷的途径就是要身处一个高水平的桥牌环境当中。非常遗憾的是，在中国的现实环境中，我估计除非你被选入了国家集训队，否则你是很难有这样的机会的。所以对于一般爱好者来说，网络是一个很好的工具。

我下面要引用Fred Gitelman 对于学习叫牌基本理论的最精彩的一段话（我经常引用他的话，因为讲得确实很好）。

Learing the basics of bridge bidding by Fred Gitelman

I am sorry, but the only good books I know of on this subject were written more than 50 years ago. Probably for some they would still be interesting to read, but the game has changed so much since then that I expect most non-experts reading such books (if they could even find a copy) would end up becoming confused.

I see most of today's books about bidding as analogous to those spam-like ads "work part time from your home and earn $100,000+ per year!" or "eat all the chocolate you want and never gain any weight!". Most modern books on bidding I have seen are nothing but hype and what they are hyping is some bidding system or collection of conventions that will "improve your results by 10% without you having to learn the basics!".

Here is what I would suggest:

Don't give a great deal of consious thought to this subject in your first few years of serious play. Learn a simple bidding system and only the few conventions that are so popular that they have essentially become part of "standard bidding" (unfortunately there are now quite a few conventions that fall into this category).

Keep your mind uncluttered with conventions that you don't really understand and play as many hands as possible, ideally with either a keen regular partner who is at roughly the same level as you or with a much better player who understands that it will help you more to spend your time discussing concepts like "a jump shift is forcing to game but a reverse is not" rather than the latest flavor of modified DONT.

Your brain is a remarkable machine. You will learn a lot of what is important by osmosis, especially if you manage to avoid distractions (like trying to come up with the best possible scheme of rescues when the 10-12 1NT opening that you shouldn't be using get doubled).

If you can afford to hire a professional player to be your partner or to give you online lessons (or whatever) you should do so, but do not hire anyone unless they are highly recommended by a person you trust and respect. If the pro or teacher starts by telling you that you must learn to play "4 of our minor is always 1430 Keycard Blackwood with specialized followups to the trump Queen ask" then find someone else - this person is trying to sell you snake oil.

After each session you play you should think about the hands and talk them over with your partner. If your partner is at the same level as you, try to make friends with an experienced player who is willing to discuss the hands you are not sure about (and who is the type of player whose idea of good advice does not involve teaching you that you would not have had a problem if you used his preferred variety of Extended 2-way Reverse Drury).

If you are fortunate enough to have access to an experienced player who is willing to help you, do not waste this opportunity by asking him questions that are designed to boost your ego (by trying to convince him/her to agree that your disaster on a particular hand was your partner's fault for example). LISTEN to your expert friend/teacher even if you disagree with him or her. Then THINK about it later. Do not get defensive when you are told that one of your bids was horrible. Instead try to understand what went wrong with your thinking process so that you can learn from your mistakes.

Once you get to the point that you consider yourself to be solid intermediate player (this should take 2 or 3 years of hard work) you should buy a subscription to The Bridge World magazine (and if you have friend who has a collection of back issues try to borrow them). Each month this magazine has a feature called The Master Solvers' Club. Read it and think about what you read. Re-read it and think about what you read.

You may find the other features of this magazine to be interesting as well, but it is fine if you read only The Master Solvers's Club in each issue.

This will help you to learn things like:

1) That bidding is not just an exercise in language, it is also an exercise in logic
2) How strong players apply logic to solve unfamiliar problems
3) The axioms that form the basis of this logic (which are "the basic principles of bidding theory" that I referred to in an earlier post)
4) You will also learn plenty about the language aspects of bidding, but most of these lessons will not involve learning the names and mechanics of new conventions.
5) That bidding situations in which the "right" answer is not at all clear are far from rare, regardless of how well you play.

This will also help you to improve your bidding judgment. Good bidding judgment is largely a function of experience. Reading what a bunch of good players have to say about a bunch of interesting bidding problems allows you to benefit from their vast experience without having to experience the same hands yourself.

Keep in mind that in many ways "learning the basics of bidding theory" is similar to things like "learning the basics of probability theory" or "learning the mechanics of compound squeezes" - these are all just parts of the game. On any given hand any given part of the game is unlikely to matter. You can survive (and you can certainly enjoy bridge) without learning such things.

All players are better at some parts of the game than others. For most parts of the game it is not necessary to be highly proficient in order to achieve reasonable results at the table.