u came in at the correct time. alot of free stuffs..

1st thing to do is max your masteries

If you ever need help on 6* Hero Selector, you can refer to HERE
Save your rubies for maxing the Mastery skills first.
You can draw heroes when you feel like it but try to focus on the mastery. It will help you progress better in the game.
You can post your IGN here. I can add and send you a free 5* hero ticket (this is one time only).

Friend request sent. Please accept.

AnythingK Sent you the free hero ticket. Good luck. 
Btw, the Hero Rate Up time is everyday 12PM ~ 2PM and 6PM ~ 12AM.
Try to use your hero tickets during those time.

Tip 1: Focus on creating your team of 6 star roster
At the beginning of the game, you will use whatever that is given to you. Once you start having stronger 5/6 heroes, you can then opt to be picky and decide what you want to do. The general rule is this:

Feed 1/2 star heroes to your 3/4/5/6 star heroes
Fuse any hero that is 3 stars or higher.
And as a fellow pro Seven Knights player says:

use 1 star units to power up 3/4/5 star units.
use 2 star units to power up 6 star units.
use 3 star units to fuse for 4 star units.
use 4 star units to fuse for 5 star units.
use 5 star units to fuse for 6 star units or rank up if it’s a desirable unit.
use 6 star units to use if it’s desirable or fodder for trans/unlock.
Also consider selling your level 30 units if you are low on gold. For the long term, fuse the 3/4/5 star units you get in the game.

I only fuse 4* and 5* cards. Feed them whatever I have.

Its easier now compared to when the game just launched. 
Now we have the Power Up Cake dungeon. You should use the Power Up cake to power up your 5*/6* Heroes.

When you are low on gold, only sell the max level 1* fodder and save the 2* for power up. Their selling price only differs by 200 gold.

For the 4* Hero fusion, its tiring but that's what we do with the max level fodder we get while farming for rubies.
You can use the 4* Hero as power up material for your 5*/6* Hero in order to conserve gold.

For the 6* Heroes, now you can use the Synthesis to exchange 2 useless 6* Heroes into 1 hero that you need. But using them to unlock weapon/armor slot is probably a more suitable choice for you now.

get a hero that can deal aoe damage for both skill. That u will use for farming.

Upgrade velika to 6* first i guess.. both her skill are AOE.. Use her for farming.. 

Rachel and dellons are 7 knights. Focus on these 2.
Velika can be used as your farmer for now, 2 AOE skill. Focus on her as well.
Sieg you will need for dragon but not a priority now. Keep him but not priority for now.
Don't think there will be any use for zhao yun and definitely no use for Jane. Keep them until u get other better units but don't focus too much on them.

You should be able to get ace from lord selector right?

It will go on until 21 days. You will get it. As long as u check in once before 31st you will get all 21 rewards. So there, you got Ace. 

Synthesis 3 useless element into 1 that you needed. Not that I recommend it though. Haha.

Do not syn 5* element is not cost effective, the most u syn is 4* element. Those old timer mostly do it with light or earth element because too many. New player should just keep all the element as there is so many hero to build.

Alternative way to get element, buy the 3* Element Selector from CR Shop, or re-enter Daily Dungeon on the particular element day. 3* (normal) cost 150 ruby per-retry and 4* (hard) is 300 ruby.

Well I wouldn't really recommend choosing a Giparang right now. But I would recommend you to pick Lina the most awesome healer in the game. She can boost your damage as well as heal you constantly for 2 turns (similar to regen skill in final fantasy series) But do know that Lina damage boosting skill does not stack with Dellons on the same team as his passive contributes the same type of boost as Lina active skill.

For jewel on Shane, basically you'll need the substat of Critical Damage %/Damage %/ Life Steal

Well if you really want to prepare yourself for dragon raid. I would suggest going for Lina as you already have Sieg in your inventory.

You can have a basic 1st team setup of:

Backliner: Shane
Front: Velika, Lina, Eileen (or Bai Jiao) & Sieg.

Since you don't have an Eileen you can opt to invest in Bai Jiao to boost your damage.

If you go for karon also not a bad idea.

You can setup like this:

Backliner: Shane
Front: Velika, Karon, Bai Jiao, Dellons.

It's kinda up to you how you like to play.

Edit - Also, IMO investing in Lina now and sieg is a good thing as in Korea, they got their awakenings (new system coming in to Asia within a few more months) in comparison to Karon.

Well I wouldn't really recommend choosing a Giparang right now. But I would recommend you to pick Lina the most awesome healer in the game. She can boost your damage as well as heal you constantly for 2 turns (similar to regen skill in final fantasy series) But do know that Lina damage boosting skill does not stack with Dellons on the same team as his passive contributes the same type of boost as Lina active skill.

For jewel on Shane, basically you'll need the substat of Critical Damage %/Damage %/ Life Steal