Any pointers for a strong relationship?

Communication, Talk, talk talk - about everything and anything - Even death and funeral arrangements or cancer etc etc.
Don't let sex be top priority or it will erode everything you've built.
Try always to see from each other's perspective, and it's ok if you don't absolutely like the same things - just don't be condescending about it or harbour nastiness - otherwise, you're harbouring destructive traits and you really should live alone (as you will find this in every person you grow with)
In ways of supporting your partner, sometimes, you might have to sacrifice your patience, or some of your time, or time with your friends, to be with this "best friend and lover" , but nothing too drastic -
As long as each partner aims at putting forth 60% to care for each other, then there's overlap for when times are super tough.
As your relationship transcends years as opposed to weeks, you start to acquire history. It can be overwhelming as you might wonder what you might be missing looking at the green grass over yonder. It's nothing, you're not missing much at all. You also will have to start ALL over again from the beginning, only to survive 3 years more with the new guy before you find out you don't like it every time he smells his fingers after he eats chicken

You should also talk to your partner about monogamy (if that is what you both seek) and revisit this subject every few years. WE men  do tend to get a tad boring, so sometimes a  relationship needs reassurance that the sex hasn't become something that isn't working anymore or is no longer "enough"  - People do change - or … People finally show their true colours....

I could go on and on. I will stop for now...

And also be yourself, take care of your partner, be honest and loyal.

Someone on Reddit sums it up well,

"According to Rudder's data, relationships are most likely to last when the couple is highly Embedded (everyone knows everyone else), but even better when they are Assimilated - The couple serves as a bond between otherwise unconnected cliques.

The power of assimilation comes from the fact that your spouse is one of the few people you introduce into the far corners of your life. […] [Your other friends,] though densely intraconnected groups themselves, are unrelated to one another but for you and your spouse.

For married people on Facebook, their spouse is the most assimilated member of their network an astounding 75 percent of the time. And even more important for assimilation as a metric of relationship strength, the young couples for whom that's not the case are 50 percent more likely to break up. In the most stable relationships, the two people play this unique role in each other's lives."  https://www.reddit.com/r/OkCupid/comments/2vc6uh/relationship_test_dataclysm/

Here's a talk Rudder gives about his work
Youtube Video

I hope this helps

communication.

Absolutely.  And, be the first one to get the communication going.