1 - Read guides:
They'll tell you which units are offensive and defensive, how to time attacks, how to build cities, how to spot colony ships etc etc
2 - Get the app:
It's rubbish to play on but having the alarm will come in handy and mean it is harder to catch you offline
3 - Join the right alliance:
Find the right one for you. Don't just join the first one to send an invite or be fooled by their ranking and think #1 alliance will be the best. Have a look for location, battle points (mainly ABP) and how active their players are (see grepointle or grepostats). Apply using well written message to recruiter, don't just use alliance finder tool or send 'add me plz' as you're more likely to be turned down.
4 - Be a team player:
There is no point joining an alliance if you do not support your team mates, 'cos when you need help you won't find as many people willing or able to help you. Also helping someone else is a good way to break the ice and the social aspect of the game is what makes it fun.
5 - Post your attack reports:
If helping someone else clear, post your battle reports on the thread. Not only shows you are helping but is a good way to learn from your mistakes. Things like attacking with biremes, sending unescorted trans, sending cats with no troops to go with them are common mistakes made by many players learning. If you post the reports, others will be able to see them and will be able to tell you what you're doing wrong and explain how to do it better.
6 - Post info clearly:
Just posting 'please help, they're trying to take my city' or 'help I'm under siege save me' are the most redundant and maddening thing to read as they give no usable information. Without city name, arrival/siege end time nobody can help you. You should be giving more info than just those two but they are essential and by reading forum when helping others, you'll pick up what info to post.
7 - Ask questions:
If you're not sure about anything, either ask on the forum or find somebody within your alliance to mentor you. Many of the vets like passing over info to newbies. Honestly most actually enjoy being asked questions, so don't be shy about asking them. When going for first conquest, if you have a mentor, they will not only help you plan it out and give you some good advice, they will be able to give you hand clearing/supporting so you'll be more likely to succeed.
8 - Be active:
If you can't log in daily, this may not be the right game for you. If you can be on daily but need to take the occasional day/week off then remember to turn on vacation mode. If not, you could come back to find that you've lost your cities and have been booted from your alliance. Also never tell anyone in enemy alliance that you're going on vac, or you could get humped.
9 - Be organized:
When you have a few cities, or are playing on a few worlds it can be hard keeping track of what you are sending, when you're sending it and where you are sending it. So if you plan things out in advance and keep a note of them. It doesn't matter if you use the notepad in game, the attack planner, a spreadsheet or a good old fashioned paper and pen as long as you you know what you're doing and when you're doing it.
10 - Have fun - Remember this is only a game. I know some days the game can be frustrating, a conquest doesn't go to plan, you lose a city, FF sinks one of your sieges etc it's easy to see red but there really is no point taking it to heart. CQs attempts can be retried, cities can be taken back and everyone makes mistakes, so just let it go. Learn from it and move on, don't dwell on it or worst rage quit.