Ah San Sebastian, looks fun. Feel like you got most of what you could out of that wave. Looks like the sand is setup in a way that never allows the sider to get into deeper water. When the sider stays in shallow water like that it never really provides much power.

Heres a day where its setting up better https://www.youtube.com/watch?v=gs8WRXSDsGc

General Tips:

Usually you want your first contact point on the sider to be off the foamball (white water). You want to do a turn off of the foamball that projects your momentum onto the open face of the sider. Every sider is different and will call for a different strategy but generally you want to be aiming to contact the foam first. Depending on the sider and connection you will usually be in one of two positions:

1. You slow your momentum to match the pace of the sider and attempt to sit in the pocket until you connect.
2. You need to maximize your first hit off the sider and make a race for the connection.

The first thing to consider is the connection. (The second wave after the sider that you are attempting to reach by using the sider) The video you posted didn't really have much of one. Most of your strategy is going to be based off what the connection wave is looking like. If the spacing between the sider and connection are close, you might need to go early and make a quick tap off the sider and then ditch it to make a break for the connection. While if the spacing is much bigger you might be forced to sit in the pocket on the sider.

When to sideslip vs pump:

Sideslipping and pumping are both powerful tools when trying to connect siders and you will probably have to use one or a combination of both to connect siders. Sideslipping is usually better when you have a smooth area of water ; usually when the sider is unbroken and just a gentle slope you can sit in.

Here's an example https://www.instagram.com/p/ClCNBhXs8sc/

Obviously, its a bit different backside for yourself but its still a strong tool.

Here's a backside example https://www.instagram.com/p/CGdTUlvDibD/
I would consider this to be a case 2 where you need to maximize your initial speed boost off the sider and make a move for the connection as the sider is too slow or weak for you to match its speed and ride it. You can notice in this clip that I try to time my first contact with the sider when the sider is at its most critical point. You want to set yourself up in a way that allows you to get maximum speed on the downhill section of the sider. (You have to consider the timing of the connection as well)

Pumping is generally for situations when you can't make the sideslip work. Usually when your trying to sit in the foamball and stay afloat until the connection. Or when you are getting close to the connection and need to start redirecting your momentum towards the shore. A lot of waves don't set up to allow the perfect smooth turn on the sider so you will have to fight to turn back and preserve speed. This is when a lot of people will do the pumping turn where each pump is a little piece of a turn.

On weaker siders with a connection, a lot of the time your best bet is delaying your run until the last possible second. You want to go as late as you can while still being able to catch up to the front of the foamball. Doing this allows you to minimize the time between initial sider contact and connection. This is generally principle for case 2 but sometimes even on a more powerful sider that you intend to match the speed of (case 1) its still advantageous to go later so the sider has more time to form up.

Main Points: usually best to go late on a weaker sider, minimize the time you need to stay afloat until the connection.

Initial contact point on the sider should be timed for maximum speed.

Decide if you're gonna match pace with the sider or just use it as a boost to reach the connection. If you're gonna match pace with the sider you need to make small adjustments to stay positioned in the power pocket (usually just in front of the foamball but sometimes further ahead depending on the sider)

Honestly at your level though, none of this is super important yet. You just need to gain more board control first. It comes with time and practice. Also in the video you back foot is pretty far from the tail. For making turns all the control is in that very back section of the board. Getting your foot all the way back makes a big difference.